The line: while( a[ 0xFULL?’\0′:-1:>>>=a<:!!0X.1P1 ] ) contains the digraphs :> and <:, which translate to ] and [ respectively, so it’s equivalent to: while( a[ 0xFULL?’\0′:-1 ] >>= a[ !!0X.1P1 ] ) The literal 0xFULL is the same as 0xF (which is hex for 15); the ULL just specifies that it’s an unsigned long … Read more
You don’t need and you should never write code like that – especially if you’re not a C compiler / standard library vendor. It is code used to implement strlen with some very questionable speed hacks and assumptions (that are not tested with assertions or mentioned in the comments): unsigned long is either 4 or … Read more
It’s a hint to the compiler that the variable will be heavily used and that you recommend it be kept in a processor register if possible. Most modern compilers do that automatically, and are better at picking them than us humans.
rand() is defined to return an integer between 0 and RAND_MAX. rand() + rand() could overflow. What you observe is likely a result of undefined behaviour caused by integer overflow.
If you compile with debug symbols (add -g to your GCC command line, even if you’re also using -O31), you can use objdump -S to produce a more readable disassembly interleaved with C source. >objdump –help […] -S, –source Intermix source code with disassembly -l, –line-numbers Include line numbers and filenames in output objdump -drwC … Read more
0.0039215689 is approximately equal to 1/255. Seeing that this is OpenGL, performance is probably important. So it’s probably safe to guess that this was done for performance reasons. Multiplying by the reciprocal is faster than repeatedly dividing by 255. Side Note: If you’re wondering why such a micro-optimization isn’t left to the compiler, it’s because … Read more
The functions in stdlib.h and stdio.h have implementations in libc.so (or libc.a for static linking), which is linked into your executable by default (as if -lc were specified). GCC can be instructed to avoid this automatic link with the -nostdlib or -nodefaultlibs options. The math functions in math.h have implementations in libm.so (or libm.a for … Read more
foo->bar is equivalent to (*foo).bar, i.e. it gets the member called bar from the struct that foo points to.
There is strtol which is better IMO. Also I have taken a liking in strtonum, so use it if you have it (but remember it’s not portable): long long strtonum(const char *nptr, long long minval, long long maxval, const char **errstr); You might also be interested in strtoumax and strtoimax which are standard functions in … Read more
I’ll interpret your question as two questions: 1) why -> even exists, and 2) why . does not automatically dereference the pointer. Answers to both questions have historical roots. Why does -> even exist? In one of the very first versions of C language (which I will refer as CRM for “C Reference Manual”, which … Read more