32- and 64-bit arithmetic functions for use with 32-bit GCC. Some versions of 32-bit GCC may emit calls to external helper functions to perform certain 32- and 64-bit operations. Normally these functions are resolved by libgcc.a which is statically linked to the program. But libgcc may not be usable in some applications, e.g. embedded systems and linux kernel drivers. In those cases you'll get an linker error such as: undefined reference to `__divdi3' The solution is to link arith64.c to your code, or just copy the required functions. Also see https://gcc.gnu.org/onlinedocs/gccint/Integer-library-routines.html. Note not all operations have been implemented, just the ones I've required to date. ==== 'make' performs Monte-Carlo validation testing. Two test executables are created, one linked to arith64.c and one to libgcc. test.py launches these into the background and then passes identical sets of random numbers to each, comparing their outputs. On mismatch it reports error and exits, otherwise it will run forever, intermittently printing the total number of tests performed. 'make bench' starts the test executables in benchmark mode, they perform each operation one million times and print the average elapsed time in nanoseconds. test.py then collates the returned information and prints a running average every 5 seconds, e.g.: 286359M : arith64 gcc abs : 2.74 2.68 ashl : 2.49 2.69 ashr : 2.87 2.74 clzd : 2.95 1.63 clzs : 2.60 1.33 ctsz : 3.50 1.42 ctzd : 3.57 1.65 div : 16.19 8.11 ffs : 2.69 1.64 mod : 15.49 8.32 popd : 6.31 3.59 pops : 2.43 2.15 shr : 2.39 2.69 udiv : 13.04 5.64 umod : 11.94 6.25 This shows that the gcc native functions, presumably written in assembly language and leveraging CPU-specific arithmetic operators, are generally twice as fast as arith64 equivalents.
Introspelliam/arith64
__udivdi3(), __divdi3(), __umoddi3(), __moddi3(), etc. for embedded GCC
CUnlicense