https://stackoverflow.com/a/28414758/1599699. I post a little adjustment 'Code B' for anyone who maybe have the same problem. Yes, it is limited to one try-catch in the same function. Penrose diagram of hypothetical astrophysical white hole, Expressing the frequency response in a more 'compact' form. In terms of the number of assembly instructions, here we go: My benchmark has had the optimization turned on. Collectives on Stack Overflow. if( rv&0x08 ) tmp |= 0x10; To automatically free other types of resources, they also add things like finalizers or context managers). The high level language code for this is much more complicated, because C and C++ do not support rotating to carry and rotating from carry. a date for which you know the day of week, e.g. This is my implementation. What you are asking is not possible in C (at least without compiler-specific extensions; it would be possible in C++, however). I'll chip in my solution, since i can't find anything like this in the answers so far. (Maybe do that in the existing answer about intrinsics). So gcc doesn't realize that rotate-counts are inherently modular. Ready to optimize your JavaScript with Rust? Devide by zero is not even an exception in C++, to handle it you need to either check the divisor is not zero and handle it or handle the SIGFPE that is thrown when you run a devide by zero formula. Collectives on Stack Overflow. Doesn't do any checking so it assumes the user will play nice. I'm rather partial to Ada's exception handling myself. Does exception handling require object-oriented programming? http://www.di.unipi.it/~nids/docs/longjump_try_trow_catch.html, github.com/php/php-src/blob/php-8.0.7/ext/bcmath/bcmath.c#L455. The AND operation (& 0x010884422010ULL) selects the bits that are in the How to make gcc generate rotate instructions? Ultimately this might even be faster than a full table. Specifically, it uses the "label as value" extension, which allows you to take the address of a label, store it in a value and and jump to it unconditionally. To do all your input with fgets even though you wanted/needed some of scanf's parsing, you can read lines using fgets and then parse them after the fact using sscanf. from the comp.lang.c FAQ. Creating a C program that determines week day of 1st date of given month in 2021. return the day of the week with day, month, year and first of January provided? 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I don't know, I think it doesn't mention it, but stdin is FILE* and fseek accepts a FILE* parameter. Assuming you want to shift right by L bits, and the input x is a number with N bits: Below is a slightly improved version of Ddac Prez's answer, with both directions implemented, along with a demo of these functions' usages using unsigned char and unsigned long long values. btw, for a DWORD (32-bit) use _rotr and _rotl. Input: exp = [()]{}{[()()]()}Output: Balanced, Input: exp = [(])Output: Not Balanced. What is the easiest way to initialize a std::vector with hardcoded elements? Returns: If r is 0, x; if r is positive, (x << r) | (x >> (N - r)); if r is negative, rotr(x, -r). A bigger issue then the variable however is the label as you can't have duplicate labels in the same function. The only difference is I don't see the need for that last "goto END", I just insert a success return at that point, a fail return after the rest. Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content, Bitshift (rotation) with hexadecimal in C, What is the equivalent of _rotl64 under GCC. Next, the author proposed 2 ways to solve such probrems: This code worked actually. the bit located at the extreme right of variable b. is this solution cross? Here is Exceptions.h: Note that this code references some additional methods that I'm not including here (because class inheritance in C is off-topic). Received a 'behavior reminder' from manager. @Harshdeep: Consider the binary encoded indexes of the table entries. Code-only answers are not useful in the long run. On the other hand using the loop will increase the execution time of the code, but the size of the code in memory will be small. If the value's not 16-bit, you silently get nonsense. Check your email for updates. Stack Overflow for Teams is moving to its own domain! Why is the federal judiciary of the United States divided into circuits? Stack memory lives in the live span of the function. has the effect of merging together each set of 10 bits Thanks for contributing an answer to Stack Overflow! This uses a global pointer so the longjmp() knows what try was last run. Are there any issues? I am teaching myself C. My goal is to make a C function that just walks a query string and splits on the ampersand and the equals sign. It was written with 8-bit microcontrollers in mind and the "year" argument is a year from 0 to 99 only (representing 2000 to 2099). These are some of the x86 options: Presumably some non-x86 compilers have intrinsics, too, but let's not expand this community-wiki answer to include them all. doesn't read only the characters before the linefeed ('\n'). Would salt mines, lakes or flats be reasonably found in high, snowy elevations? I think this answer is the opposite of simple. The most compiler-friendly way to express a rotate in C and C++ that avoids any Undefined Behaviour seems to be John Regehr's implementation. If I use this code to do something like. Does not work on Linux. Now take an OR between 14 time left shifted value and 2 times right shifted value. Your information seems to be superficial as you commented on the code I wrote. The program will not work properly because at Line 1, when the user presses Enter, it will leave in the input buffer 2 character: Enter key (ASCII code 13) and \n (ASCII code 10). When i put those back in. :). What mathematical formula can I use to get the day (e.g. - with a single entry and single exit point) also makes it very easy to insert pre and post ("finally") logic that will execute no matter what. I think you can find that in glib: CONS: It is not reusable code, it is only for 8051, unsigned char reverse(unsigned char rv) Where is it documented? ), @mirabilos: The common compilers work fine with your idiom, IIRC, but they would be allowed to make demons fly out of your nose if they wanted to with a count of, I was going to say "just use portable-snippets" but then I checked the code and it seems to (a) invoke UB for, How come bit rotations took so long to land in modern c++? That's not the same thing. i.e. Usage: For that, you'll have to substring out the new digit/letter and do string concats instead of simply adding each time. ", it can be really frustrating when all the answers are, "You shouldn't want to do X." Another solution not mentioned yet is to use: What happens if you score more than 99 points in volleyball? What is the algorithm to generate this table? Why would Henry want to close the breach? Instead, you'd probably want to break those out into self contained sub functions that similarly handle errors, initialize + finalize explicitly like this. error when using malloc() and free() function, *** Error: double free or corruption (out): 0x00007fffe3465010 ***.Warning: Corrupted shared library list: 0x7ffea4000920 != 0x7ffff7ffd9d8. So if you have a const char* ready, just go ahead with using that variable name directly, as shown below [I am also showing the usage of the unsigned long variable for a larger hex number. @fake-name '> so the C++11 version won't work on windows unless you change that to something else' Yeah, change that to linux. "[m] + d) % 7; The basic idea underlying all of these methods is the same: boil the date down to a monotonically-increasing sequence of day numbers (taking month lengths and leap years into account), then reduce that day number modulo 7. I don't know from where you got that idea about. This answer seems to be the best and portable, see how php/bcmath uses it: version 1 is nice idea, but that __HadError variable would need to be reset or scoped. Check your email for updates. The multiply operation (b * 0x0202020202ULL) creates five separate copies of the 8-bit byte pattern to fan-out into a 64-bit value. A portable way to clear up to the end of a line that you've already tried to read partially is: This reads and discards characters until it gets \n which signals the end of the file. In the United States, must state courts follow rulings by federal courts of appeals? Why is the federal judiciary of the United States divided into circuits? Connect and share knowledge within a single location that is structured and easy to search. I can not say that it is the fastest or the most efficient, but it ought to be one of the cleanest. Concentration bounds for martingales with adaptive Gaussian steps. And for interactive input it's not guaranteed to do anything. rewind(stdin); before the line reading the input is the only guaranteed method. If you find yourself needing to "flush input", you have already lost. How many transistors at minimum do you need to build a general-purpose computer? @user964491 But note that the answer you accepted is. See this other question: What can I use for input conversion instead of scanf? This is particularly useful in environments that operate a lot on the bit level (like microcontrollers). So a rotate can fold into a register-source operand for an EOR instruction or something. Connect and share knowledge within a single location that is structured and easy to search. Have one assembly language module for each target platform. A carefully-written GNU C inline-asm rotate would allow the count to be an immediate operand for compile-time-constant shift counts, but it still couldn't optimize away entirely if the value to be shifted is also a compile-time constant after inlining. Not the answer you're looking for? Of course, those are not pointers allocated by malloc() (or similar), so free()ing them is undefined behavior. Programs allocate blocks from the heap by calling the malloc function. https://gcc.gnu.org/wiki/DontUseInlineAsm. Please explain. @SurajSunny: Please consider editing your answer to include a summary of the information provided in the youtube link. scanf is a strange function, and there's a classic line from the movie WarGames that's relevant: "The only winning move is not to play". Could you detail why the well known line is a possible infinite loop? Yes, it is simple. where %*c accepts and ignores the newline, one more method I had a similar issue and noted that the default cmd on Windows Server 2012, was running the x64 one.. For Windows 11, Windows 10, Windows 7, Windows 8, Windows Server 2008 R2 or Windows Server 2012, run the following commands as Administrator:. How long does it take to fill up the tank? I just became a member, it will be interesting to see how much information/experience other members of the StackOverflow site have. What is this fallacy: Perfection is impossible, therefore imperfection should be overlooked. Excellent! Of course, both stat() and access() rely on being able to access the If your compiler supports words longer than 64 bits, the method is straightforward to extend. where X and Y are either code snippets supplied as strings or function names. If the current character is a starting bracket (( or { or [) then push it to stack.If the current character is a closing bracket () or } or ]) then pop from stack and if the popped character is the matching starting bracket then fine else brackets are not balanced. C itself doesn't support exceptions but you can simulate them to a degree with setjmp and longjmp calls. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Fun fact: ARM doesn't really have dedicated shift/rotate instructions, it's just MOV with the source operand going through the barrel-shifter in ROR mode: mov r0, r0, ror r1. In C, you can "emulate" exceptions along with automatic "object reclamation" through manual use of if + goto for explicit error handling. Count the number of set bits in a 32-bit integer. That is the closest equivalent of exceptions you can get in C. Ok, I couldn't resist replying to this. Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content. rev2022.12.9.43105. When you call std::stringstream().swap(m) I expect any memory it allocated during the How can operations like "Rotate Left" and "Rotate Right" be performed? s[] = { 'a', 'b', 'c', '\0' }, t[] = { 'a', 'b', 'c' }; The contents of the arrays are modifiable. It is quite simple. Therefore, at Line 2, it will read the \n and will not wait for the user to enter a character. The C runtime library will take care of that for you: your program will see just '\n' for newlines. How is the FP stdin behave? Irreducible representations of a product of two groups. I really like this one a lot because the compiler automatically handle the work for you, thus require no further resources. It worked for me on MSVC2012 but didn't in MacOSX Clang compiler. In that case, int, is 2 bytes.However, implementations are free to go beyond that minimum, as you will see that By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Subtraction doesn't work on unsigned values. with these defines (matching struct tm of time.h): This is question 20.31 in the C FAQ list. @Rajesh Yes, you are correct. The code probably contains both compile errors and logic errors - so while you're free to use it as you choose, TEST it before using it ;). Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Exception-like mechanisms are not going to be generally useful without a mechanism to automatically free resources when the stack is unwound. On my Core2 a cache line is 64 bytes wide, the full table would span multiple lines, whereas the smaller table easily fits one a single line. relative positions within any 10-bit set. clue me in: I thought that try catch clauses allowed you to catch exceptions (like dividing by zero). In the United States, must state courts follow rulings by federal courts of appeals? @Nobody: I already commented 5 years ago that you shouldn't use signed integer types. It reads all the characters in the stream (and discards them) up to and including the next linefeed (or EOF is encountered). Quoting from the man page of bind(). cool. A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400. At what point in the prequels is it revealed that Palpatine is Darth Sidious? if so, in the input buffer still remains the '\n' character? x86 (32 bit) Open C:\Windows\SysWOW64\cmd.exe Run the command powershell Set In that case, I believe that for all intents and purposes you cannot meet this goal based around scanf. But perhaps your goal is to do better. Why is the eastern United States green if the wind moves from west to east? struct eg_struct { unsigned char abc; unsigned int xyz; } When the structure is declared as above on a 16 bit architecture, the variable abc would be assigned some address. I've also highlighted the same 0-7 on the hex side to help with the visualization of it. Therefore, at Line 2, it will read the \n and will not wait for the user to enter a character. Even in LLVM clang, there just have been intrinsics just a few years ago =>, @sandthorn: I think the C++ and C committees have a very optimistic view of the idea that compilers should be able to recognize portable idioms (like. rev2022.12.9.43105. strsep() doesn't allocate memory, it only returns pointers inside the original string. Therefore, the conversion from time_t to unsigned int is not guaranteed! You are reading input using scanf, and it is leaving the user's newline on the input stream, and that stray newline is wrongly getting read by a later call to getchar or fgets. 16 - 2 = 14, Now right shift the value 33602, 2 times as required. You can try, but it's like putting a onesie on a squirming baby: after getting both legs and one arm in, while you're trying to get the second arm in, one leg will have wriggled out. @Lance Just count from 0 to 255 and reverse each byte by any known method. WebNOIZ (NOIZ) Token Tracker on Etherscan shows the price of the Token $0.0296, total supply 400,000,000, number of holders 340 and updated information of the token. How does legislative oversight work in Switzerland when there is technically no "opposition" in parliament? Copypasting from there is obviously simple to implement. Probably the most logical, consists in rotating the byte while applying a mask on the first bit (n & 1): As the length of an unsigner char is 1 byte, which is equal to 8 bits, it means we will scan each bit while (byte_len--), We first check if b as a bit on the extreme right with (b & 1); Am I misunderstanding something?? @H2CO3 Unnecessary copy? index b0000(0) -> b0000(0x0) boring; If we're talking about something that's simple to implement without copying a ready-made solution, creating the lookup table does still require another solution. @101010 I would expect this to be much less efficient that calling m.str({}), as Zhang's comment said.To clarify: When you call m.str({}) I would expect that it would reuse some of the memory it allocated during the first operation to speed up the next operation. (@viktor-sehr no, it will not, rev is different from bs). What you call "Enter key" is the carriage return character (. Should I give a brutally honest feedback on course evaluations? Also, I feel obligated to discourage you from using scanf entirely: Why does everyone say not to use scanf? I think they will get the idea if all 3 answers remain on this thread. This a complete, ready-to-compile example with the requisite headers. You may be interested in std::vector (that is bit-packed) and std::bitset, EDIT: I owe you a solution using std::vector. (from positions 0-9, 10-19, 20-29, ) in the 64-bit value. This function uses some of the standard library functions instead of writing your own bit manipulator. Best practices for circular shift (rotate) operations in C++, Near constant time rotate that does not violate the standards, recognized for variable-count rotates since gcc4.9, supported for variable-count rotates since ICC13 or earlier, source operand going through the barrel-shifter in ROR mode, especially MSVC-style because it forces inputs to be stored/reloaded, https://gcc.gnu.org/wiki/DontUseInlineAsm, http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0553r4.html. Then all adjacent pairs are swapped and then all adjacent single bits. This question is about how about clearing the remaining input from stdin. If it works on your system, great; if not, then it is not surprising as nothing guarantees that it will work when standard input is an interactive device (or a non-seekable device like a pipe or a socket or a FIFO, to name but a few other ways in which it can fail). Japanese girlfriend visiting me in Canada - questions at border control? Using a single global variable for your, Threading. array_2d_fill_from_user_input_scanf_and_getc.c, https://en.cppreference.com/w/c/io/fscanf#Notes. Placed table in ROM on a PIC (with addition of rom keyword). negative or if additive-expression is greater than or equal to the Don't do that. Is it possible to hide or delete the new Toolbar in 13.1? uses an if/else to skip the code block to the catch block which check the local We are using abusing the stack so child functions can also have a try/catch block. Why on earth are there all the backslashes at the ends of the lines in the code? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. However, you don't need a full lookup table. QGIS expression not working in categorized symbology. Is it possible to hide or delete the new Toolbar in 13.1? The range of int must be at least -32767.. When i take out the free(token) and free(tk). It gets every bit in the byte, and shifts it accordingly, starting from the first to the last. http://developer.gnome.org/glib/unstable/glib-Date-and-Time-Functions.html#g-date-get-day, This one works: I took January 2006 as a reference. What's the best way to check if a file exists in C? Not able to understand the location of EOF in stdin. I started building it as a template but decided halfway through to not do so too many > <, @andand For extra extra pendantry, replace. Is it appropriate to ignore emails from a student asking obvious questions? This one helped me with 8x8 dot matrix set of arrays. The second example requires c++0x extension (to initialize the array with {}). It's an exercise. Not the answer you're looking for? Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. @ishmael Your comment doesn't make sense since pressing Enter isn't required to. Anyway I don't like the answer myself: I think this is a case where binary arithmetic and shift operators are better suited. From where did you get the idea that you need to free(token) and free(tk)? You're trying to free the inside of a block of memory. Instructions: goto is great for this scenario. Did the apostolic or early church fathers acknowledge Papal infallibility? By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. You are setting up other programmers for failure because they will likely not notice the hack and try using them like C++ try/catch blocks. In reality you may choose to add a prompt asking a user to hit ENTER to continue (or, optionally, hit Ctrl-D or any other button to finish or to perform other code): There is still a problem. CGAC2022 Day 10: Help Santa sort presents! Nothing as straightforward and elegant as C++/Java's try/catch. This is similar to, but not a duplicate of this C question. Why does the distance from light to subject affect exposure (inverse square law) while from subject to lens does not? By using our site, you One could see if a compiler optimization simplifies into a suitable assembly instruction. Why use apparently meaningless do-while and if-else statements in macros? if so, in the input buffer still remains the '\n' character??? The most-upvoted answers here and here both do this with: I think a clearer (more-readable) way is to do it like this. way easier then the accepted answer. Find centralized, trusted content and collaborate around the technologies you use most. Ready to optimize your JavaScript with Rust? What properties should my fictional HEAT rounds have to punch through heavy armor and ERA? I tend to do something similar. Thanks for the letting me know about my mistake :). Is there any reason on passenger airliners not to have a physical lock between throttles? This will hang waiting for the user to press Enter. OK, I got this. Algorithm: Declare a character stack S.; Now traverse the expression string exp. In particular, if you want to distinguish between different types of exceptions, you'll need to realize that this code assumes that Object_IsSomeTypeOf(new(ExceptionSubtype1), Exception) returns true and Object_IsSomeTypeOf(new(ExceptionSubtype1), ExceptionSubtype2) returns false, and you'll need to either make your own version of my Object_IsSomeTypeOf macro or replace it with something else. C++ uses RAII; Java, C#, Python, etc. The type of c must be int (or larger) in order to be able to hold the value EOF. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. long jump out of the current function to the try block. The one liner : bind() to own address, connect() to remote address. Find centralized, trusted content and collaborate around the technologies you use most. Can I throw (and possibly catch) an exception in plain C (GCC)? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. How is the merkle root verified if the mempools may be different? I tested it on both Debian and Fedora. Why it should be SEEK_END? Where does the idea of selling dragon parts come from? Something can be done or not a fit? From your URL: 32 bit CPU: b = ((b * 0x0802LU & 0x22110LU) | (b * 0x8020LU & 0x88440LU)) * 0x10101LU >> 16; @Joshua: That's my personal favourite as well. How can I flush stdin in C? That way if I want to add some "finally" logic to any function I always easily can without needing to worry there is some other hidden returns lurking somewhere. regarding the bit-reflected lookup table for all 256 bytes, with just a few loops, you can generate it from scratch on the fly very quickly (the mapping from hex to bytes should be trivial) : This is the easiest approach to remember to me as a developer: Thanks for contributing an answer to Stack Overflow! Or you can modify the original string if you want (hint: char value 0 is the null terminator and tells functions like printf to stop reading the string). Right-shifts of negative signed integers is implementation-defined behaviour in C.). Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content. Do bracers of armor stack with magic armor enhancements and special abilities? Although probably not portable, I would use assembly language. See the context in these files for when clearing stdin might be most-useful: Note to self: I originally posted this answer here, but have since deleted that answer to leave this one as my only answer instead. It is endless loop. This simple function uses a mask to test each bit in the input byte and transfer it into a shifting output: Assuming that your compiler allows unsigned long long: This one is based on the one BobStein-VisiBone provided. @Arkku what I meant is write a script which outputs the table of the first 256 bytes and their reverse mapping. How long does it take to fill up the tank? (Unlike x86, where shifts mask the count the same as rotates). Why does the distance from light to subject affect exposure (inverse square law) while from subject to lens does not? Making statements based on opinion; back them up with references or personal experience. The contents will be unchanged to the minimum of the old and the new sizes. always flatten your bools. I have also included a helper function for easily displaying the bit patterns. This code duplicates the error handling logic in multiple places and may do incorrect things like calling fclose(fp) multiple times. WebIn computer programming, an integer overflow occurs when an arithmetic operation attempts to create a numeric value that is outside of the range that can be represented with a given number of digits either higher than the maximum or lower than the minimum representable value.. cprogramming.language-tutorial.com/2012/01/, http://developer.gnome.org/glib/unstable/glib-Date-and-Time-Functions.html#g-date-get-day. But my first question is: Why the second getchar() (ch2 = getchar();) does not read the Enter key (13), rather than \n character? You use goto in C for similar error handling situations. Let build process choose the modules. Code rotate right r0 cross carry and then rotate carry left to r1. What can I use for input conversion instead of scanf? 1 ^ 0 = 1, 0 ^ 0 = 0, etc. Only then will they break out of the while loop. Version 1 is a local throw only (can't leave the function's scope). The bit arith is cheap and the table easily fits on a cache line. @EvAlex: there are many issues with this. On x86, this version inlines to a single rol r32, cl (or rol r32, imm8) with compilers that grok it, because the compiler knows that x86 rotate and shift instructions mask the shift-count the same way the C source does. codegolf.stackexchange.com/questions/36213/, graphics.stanford.edu/~seander/bithacks.html#BitReverseTable, Rich Schroeppel in the Programming Hacks section, aldeid.com/wiki/X86-assembly/Instructions/rol, quick-bench.com/q/Hs10lka2Xj1Y9SyQkgwSkeJ1M44. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, I believe you always need some anchor, i.e. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Is it cheating if the proctor gives a student the answer key by mistake and the student doesn't report it? Look here for other solutions that might work better for you. Should teachers encourage good students to help weaker ones? I think Cray's did (used floating point registers with padding where exponent field would be). length is 16 right shift value is 2 If you typed a character and pressed enter, then that input character would be read by line 1, and then '\n' would be read by line 2. (gcc for x86 targets does arithmetic right shifts, shifting in copies of the sign-bit rather than zeroes, leading to a problem when you OR the two shifted values together. According to the 1999 ISO C standard (C99), size_t is an unsigned integer type of at least 16 bit (see sections 7.17 and 7.18.3). Is it cheating if the proctor gives a student the answer key by mistake and the student doesn't report it? While this code may answer the question, it would be better to include some context, explaining how it works and when to use it. Because in the while statement, we use getchar() != '\n', that means read any single character except '\n'?? It is a bit overengineered maybe, but it generates the lookup table using C++14 std::index_sequence in compile time. @Rajesh That would clear until the input stream is closed, which it won't be if there is more input to come later. What are 0x01 and 0x80 representative of in C bitwise operations? How do I clear stdin before requiring input if stdin is not clear in C? This function just makes a local var so it knows if there was an error and uses a goto to jump to the catch block. What's the difference between "STL" and "C++ Standard Library"? "Scene-graph of layered 2D interface elements manipulated in 3D space via position, grouping, transparency, scaling, clipping and rotation." If you want dates before 01-01-1900, you could easily change the anchor to the starting date of the Gregorian calendar. (I think this is what lua uses internally). Tabularray table when is wraped by a tcolorbox spreads inside right margin overrides page borders. Should I use fflush like presented? I suppose that other suggested algorithms have such an anchore built-in. On the other hand, the declaration. WebFrom Wikipedia:. While there are multiple ways to reverse bit order in a byte, I'm curious as to what is the "simplest" for a developer to implement. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. As the author of the above code have explained: Several notes: The result of a shift operation is undefined if additive-expression is @wilhelmtell - you'd need a table to know which ones are the palindromes. If you think it was me who down-voted your answer, you're wrong. you should wrap x into parentheses to avoid nasty surprises with expressions as argument to the macro. Is the EU Border Guard Agency able to tell Russian passports issued in Ukraine or Georgia from the legitimate ones? Warning: the following is not very nice but it does the job. The Standard C++ Way Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, @mirabilos: Your version has UB with bits=32, count=32, in the shift by, @mirabilos: Right, but our goal is to write a function that feeds the shift count directly to a single asm instruction, but avoids UB on a C level for any possible shift count. Web"Developed in C, with language bindings for Perl, Python, C#, C++, Vala and Ruby." Find centralized, trusted content and collaborate around the technologies you use most. Not exactly clearing the input buffer but it works just fine. See. For example, nesting multiple error handling stacks within one function this way isn't very clean. There are many ways to reverse bits depending on what you mean the "simplest way". I come from the Java world where you can catch a general exception. Just because something is an address doesn't mean that you need to or should free it. The fastest code to use is the Look Up Table (LUT). I'll present it using an example: If you so wish, you could refactor common code in defines, effectively implementing your own error-handling system. Please check below code snippets to remember and understand even better this solution where we move half by half: NB: The >> 4 is because there are 8 bits in 1 byte, which is an unsigned char so we want to take the other half, and so on. OTOH, on these systems, we could enhance the definition of "heap" to mean the memory area First the left four bits are swapped with the right four bits. How to return multiple values from a function in C or C++? In case 2, the better solution is, never use scanf("%c"). Let me first say I don't think it's a good idea to simulate this in C as it really is a foreign concept to C. We can use abuse the preprocessor and local stack variables to give use a limited version of C++ try/throw/catch. What is this fallacy: Perfection is impossible, therefore imperfection should be overlooked. The C language imposes some requirements on the ranges of these types. How can I clear previous output in Terminal in Mac OS X? WebSecure your applications and networks with the industry's only network vulnerability scanner to combine SAST, DAST and mobile security. When you have in fact allocated a block of memory, you can only free it from the pointer returned by malloc. The compiler doesn't know what the pointer is pointing to. if( rv&0x02 ) tmp |= 0x40; Thirty days has September, April, June and November; all the rest have thirty-one, saving February alone, which has twenty-eight, rain or shine, and on leap years, twenty-nine. I have written a function (and tested it too) which gets input from stdin and discards extra input (characters). variable to see if it should catch. @jamesdlin On Linux, getchar() will wait for the user to press Enter. unsigned char tmp=0; Connect and share knowledge within a single location that is structured and easy to search. Concentration bounds for martingales with adaptive Gaussian steps. If you would like, I can edit this to show the simple assembly language. Why is apparent power not measured in watts? Or you could encode these rules to do some arithmetic in a really long single line: EDIT: note that this solution only works for dates after the UNIX epoch (1970-01-01T00:00:00Z). if( rv&0x40 ) tmp |= 0x02; Why does the USA not have a constitutional court? Seems that my slower shifting method was limiting performance in an embedded app. multiplying r by 2 with (r << 1). To make this code work for you, you'll have to understand this code well enough to replace a few things. rev2022.12.9.43105. What happens if I change them to l >= INT_MAX and l <= INT_MIN to clear the warnings? Together the multiply and the AND operations copy the bits from the original There are two main types of memory you seem to be confusing - stack memory and heap memory. You can avoid strdup() and free() altogether by simply writing char *s = p;. If p is NULL, the call is equivalent to PyMem_Malloc(n); else if n is equal to zero, the memory block is resized but is not freed, and the returned pointer is Do bracers of armor stack with magic armor enhancements and special abilities? Constraints: T is an unsigned integer type (3.9.1 [basic.fundamental]). Can we use SEEK_SET instead? Some compilers provide intrinsics for rotates, which is far better than inline-asm if the portable version doesn't generate good code on the compiler you're targeting. How can I fix it? It has arrived! Check this link. Integer constants can be written as binary constants, consisting of a sequence of 0 and 1 digits, prefixed by 0b or 0B. See elsewhere for answers that execute in O(log n) time. If you had a little experience with code execution time and how code is assembled, you would know that my code is faster. Unfortunately, it will not work with MSVC but if using only GCC/Clang is an option, then you might consider it. On ARM C, long and int are 32-bit signed Basic data types in ARM C and C++ What properties should my fictional HEAT rounds have to punch through heavy armor and ERA? Thanks for contributing an answer to Stack Overflow! Also, I've looked up malloc and it seems that it does, in fact, allocate heap memory. Now, I realize I still haven't answered the question you actually asked. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. You will notice a theme running through all three cases I listed: they all began with "You are reading input using scanf". Also, the second method depends on the condition like newline,null character,EOF etc(above it was newline), Please add a bit more details about how this solution works and how it is a useful way to solve the problem. byte so they each appear in only one of the 10-bit sets. ishmael : All of our computers here in Cyber Command are Linux and it works fine on them. rev2022.12.9.43105. If X runs into an error, Y (usually error-handling) will be executed instead. DISCLAIMER: The above code was written without any testing whatsoever. You can write a script/program to generate the table for you, and the lookup operations would be faster than any of the bit-reversing algorithms here (at the cost of having to store the lookup table somewhere). (It is a Sunday). When enter is pressed, that signals the end of the line but the stream contains a line feed instead since that's the normal end-of-line marker for the system. If there is nothing on stdin to flush when this gets called, it will block(hang) due to it being caught in an infinite loop. What is this fallacy: Perfection is impossible, therefore imperfection should be overlooked. Rotation doesn't make sense on signed integer types anyway. A code example which uses the expression follows: The expression uses the comma operator, as discussed in this answer. Need to modify it to account for shifts greater than the length of the bitset. scanf has many problems, and one of its many problems is that its error handling is terrible. A std::popcount was also added to count the number of 1 bits: How to count the number of set bits in a 32-bit integer? I am getting stuck on this error from Valgrind. Doesn't get hung in an infinite loop when there is nothing on stdin to flush like the following well know line: A little expensive so don't use it in a program that needs to repeatedly clear the buffer. If a is either an array of char, unsigned char or signed char you do not need to use sizeof twice since a sizeof expression with one operand of these types do always result to 1. 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Is it correct to say "The glue on the back of the sticker is dying down so I can not stick the sticker to the wall"? Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. Visual Studio for example _rotr8, _rotr16. cppreference says that the usage will be like: I'll give it a try when support arrives to GCC, GCC 9.1.0 with g++-9 -std=c++2a still doesn't support it. When you're done with s altogether, you should free it, but you do not have to do that with the return values of strsep. If it's OR it's not exclusive, thus it'll always be 1. For example: Of course, this isn't as elegant as C++ exceptions + destructors. Again a more realistic version of this would include some way to store error information into the exception_state, better handling of MAX_EXCEPTION_DEPTH (maybe using realloc to grow the buffer, or something like that). Is it appropriate to ignore emails from a student asking obvious questions? The simplest way is probably to iterate over the bit positions in a loop: For the very limited case of constant, 8-bit input, this method costs no memory or CPU at run-time: I used this for ARINC-429 where the bit order (endianness) of the label is opposite the rest of the word. and the adjustment was to 'catch' the (n-1) character just before the conditional in the while loop be evaluated, here is the code: The possible explanation is that for the while loop to break, it has to assign the value '\n' to the variable y, so it will be the last assigned value. Sure, there is assert and other tricks but nothing like try/catch, that also catch the raised exception. Actually i have the same problem that i cant use t2o or more than try catch in one scope, do u have solution for it ? @JensGustedt This is exactly what goto is currently used for very often and example where it makes sense (setjmp/ljmp is better alternative, but label+goto is. If your goal of "flushing" stdin is to remove all chars sitting in the stdin buffer, then the best way to do it is manually with either getchar() or getc(stdin) (the same thing), or perhaps with read() (using stdin as the first argument) if using POSIX or Linux. Not the answer you're looking for? @GrpahicsMuncher Unnecessary because the allocated memory isn't used outside the function. Better, put the function into a separate translation unit. It reports that i am not leaking anymore but the program won't run. That worked. Friday) from a given date? Is the EU Border Guard Agency able to tell Russian passports issued in Ukraine or Georgia from the legitimate ones? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, To be clear, "Enter key" is not a character. 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