Brian Hurt <bhurt@xxxxxxxxxxxxxxxxxx> writes: > So I'm looking at using gcc in an embedded environment, and providing > my own libgcc (long story). So I was looking at the libgcc > documentation at: > > http://gcc.gnu.org/onlinedocs/gccint/Integer-library-routines.html#Integer-library-routines > > which gives the prototype for __umoddi3 and __umodti3 as: > unsigned long __umoddi3 (unsigned long a, unsigned long b) > unsigned long long __umodti3 (unsigned long long a, unsigned long long b) Those prototypes are literally wrong on many, even most, systems. To interpret them correctly, you have to understand the earlier paragraph: http://gcc.gnu.org/onlinedocs/gccint/Libgcc.html#Libgcc These routines take arguments and return values of a specific machine mode, not a specific C type. See Machine Modes, for an explanation of this concept. For illustrative purposes, in this chapter the floating point type float is assumed to correspond to SFmode; double to DFmode; and long double to both TFmode and XFmode. Similarly, the integer types int and unsigned int correspond to SImode; long and unsigned long to DImode; and long long and unsigned long long to TImode. > Now, things work correctly, so this isn't a bug with the compiler- > it's the documentation which is unclear. I see two possibilities: > > 1) The prototypes on that website are just wrong- __umoddi3 is always > called to to do long long modulo. In this case, is __umodti3 ever > even used? > > 2) __umodsi3 handles 32-bit words on all systems (ignoring weird > systems for the moment), __umoddi3 handles 64-bit words- longs on > 64-bit systems, long longs on 32-bit systems, and __umodti3 handles > 128 bit words- long long on 64-bit systems and not used on 32-bit > systems. The latter is basically correct. __umodsi3 always handles 32-bit values. __umoddi3 always handles 64-bit values. __umodti3 always handles 128-bit values. (In saying this I am ignoring targets which do not use 8-bit bytes). The proper prototypes are thus target-dependent, since the sizes of int, long, and long long are target dependent. For what it's worth, the correct prototypes can be written using the __attribute__ ((mode (XX))) extension. Ian
