From: Daniel Engel <g...@danielengel.com>
This patch revision is based on comments received against: <https://gcc.gnu.org/pipermail/gcc-patches/2021-January/562917.html> As one point of comparison, a test program [1] links 916 bytes from libgcc with the patched toolchain vs 10276 bytes with gcc-arm-none-eabi-9-2020-q2 toolchain. That's a 90% size reduction. I have extensive test vectors [2], and this patch pass all tests on an STM32F051. These vectors were derived from UCB [3], Testfloat [4], and IEEECC754 [5], plus many of my own generation. There may be some follow-on projects worth discussing: * The library is currently integrated into the ARM v6m multilib only. It is likely that some of the architectures would benefit from these routines. However, I have NOT profiled the existing implementations (ieee754-sf.S) to estimate where improvements may be found. * GCC currently lacks test for some functions, such as __aeabi_[u]ldivmod(). There may be useful bits in [1] that can be integrated. On Cortex M0, the functions have (approximately) the following properties: Function(s) Size (bytes) Cycles Stack Accuracy __clzsi2 50 20 0 exact __clzsi2 (OPTIMIZE_SIZE) 22 51 0 exact __clzdi2 8+__clzsi2 4+__clzsi2 0 exact __clrsbsi2 8+__clzsi2 6+__clzsi2 0 exact __clrsbdi2 18+__clzsi2 (8..10)+__clzsi2 0 exact __ctzsi2 52 21 0 exact __ctzsi2 (OPTIMIZE_SIZE) 24 52 0 exact __ctzdi2 8+__ctzsi2 5+__ctzsi2 0 exact __ffssi2 8 6..(5+__ctzsi2) 0 exact __ffsdi2 14+__ctzsi2 9..(8+__ctzsi2) 0 exact __popcountsi2 52 25 0 exact __popcountsi2 (OPTIMIZE_SIZE) 14 9..201 0 exact __popcountdi2 34+__popcountsi2 46 0 exact __popcountdi2 (OPTIMIZE_SIZE) 12+__popcountsi2 17..401 0 exact __paritysi2 24 14 0 exact __paritysi2 (OPTIMIZE_SIZE) 16 38 0 exact __paritydi2 2+__paritysi2 1+__paritysi2 0 exact __umulsidi3 44 24 0 exact __mulsidi3 30+__umulsidi3 24+__umulsidi3 8 exact __muldi3 (__aeabi_lmul) 10+__umulsidi3 6+__umulsidi3 0 exact __ashldi3 (__aeabi_llsl) 22 13 0 exact __lshrdi3 (__aeabi_llsr) 22 13 0 exact __ashrdi3 (__aeabi_lasr) 22 13 0 exact __aeabi_lcmp 20 13 0 exact __aeabi_ulcmp 16 10 0 exact __udivsi3 (__aeabi_uidiv) 56 72..385 0 < 1 lsb __divsi3 (__aeabi_idiv) 38+__udivsi3 26+__udivsi3 8 < 1 lsb __udivdi3 (__aeabi_uldiv) 164 103..1394 16 < 1 lsb __udivdi3 (OPTIMIZE_SIZE) 142 120..1392 16 < 1 lsb __divdi3 (__aeabi_ldiv) 54+__udivdi3 36+__udivdi3 32 < 1 lsb __shared_float 178 __shared_float (OPTIMIZE_SIZE) 154 __addsf3 (__aeabi_fadd) 116+__shared_float 31..76 8 <= 0.5 ulp __addsf3 (OPTIMIZE_SIZE) 112+__shared_float 74 8 <= 0.5 ulp __subsf3 (__aeabi_fsub) 6+__addsf3 3+__addsf3 8 <= 0.5 ulp __aeabi_frsub 8+__addsf3 6+__addsf3 8 <= 0.5 ulp __mulsf3 (__aeabi_fmul) 112+__shared_float 73..97 8 <= 0.5 ulp __mulsf3 (OPTIMIZE_SIZE) 96+__shared_float 93 8 <= 0.5 ulp __divsf3 (__aeabi_fdiv) 132+__shared_float 83..361 8 <= 0.5 ulp __divsf3 (OPTIMIZE_SIZE) 120+__shared_float 263..359 8 <= 0.5 ulp __cmpsf2/__lesf2/__ltsf2 72 33 0 exact __eqsf2/__nesf2 4+__cmpsf2 3+__cmpsf2 0 exact __gesf2/__gesf2 4+__cmpsf2 3+__cmpsf2 0 exact __unordsf2 (__aeabi_fcmpun) 4+__cmpsf2 3+__cmpsf2 0 exact __aeabi_fcmpeq 4+__cmpsf2 3+__cmpsf2 0 exact __aeabi_fcmpne 4+__cmpsf2 3+__cmpsf2 0 exact __aeabi_fcmplt 4+__cmpsf2 3+__cmpsf2 0 exact __aeabi_fcmple 4+__cmpsf2 3+__cmpsf2 0 exact __aeabi_fcmpge 4+__cmpsf2 3+__cmpsf2 0 exact __floatundisf (__aeabi_ul2f) 14+__shared_float 40..81 8 <= 0.5 ulp __floatundisf (OPTIMIZE_SIZE) 14+__shared_float 40..237 8 <= 0.5 ulp __floatunsisf (__aeabi_ui2f) 0+__floatundisf 1+__floatundisf 8 <= 0.5 ulp __floatdisf (__aeabi_l2f) 14+__floatundisf 7+__floatundisf 8 <= 0.5 ulp __floatsisf (__aeabi_i2f) 0+__floatdisf 1+__floatdisf 8 <= 0.5 ulp __fixsfdi (__aeabi_f2lz) 74 27..33 0 exact __fixunssfdi (__aeabi_f2ulz) 4+__fixsfdi 3+__fixsfdi 0 exact __fixsfsi (__aeabi_f2iz) 52 19 0 exact __fixsfsi (OPTIMIZE_SIZE) 4+__fixsfdi 3+__fixsfdi 0 exact __fixunssfsi (__aeabi_f2uiz) 4+__fixsfsi 3+__fixsfsi 0 exact __extendsfdf2 (__aeabi_f2d) 42+__shared_float 38 8 exact __truncsfdf2 (__aeabi_f2d) 88 34 8 exact __aeabi_d2f 56+__shared_float 54..58 8 <= 0.5 ulp __aeabi_h2f 34+__shared_float 34 8 exact __aeabi_f2h 84 23..34 0 <= 0.5 ulp Copyright assignment is on file with the FSF. Thanks, Daniel Engel [1] // Test program for size comparison extern int main (void) { volatile int x = 1; volatile unsigned long long int y = 10; volatile long long int z = x / y; // 64-bit division volatile float a = x; // 32-bit casting volatile float b = y; // 64 bit casting volatile float c = z / b; // float division volatile float d = a + c; // float addition volatile float e = c * b; // float multiplication volatile float f = d - e - c; // float subtraction if (f != c) // float comparison y -= (long long int)d; // float casting } [2] http://danielengel.com/cm0_test_vectors.tgz [3] http://www.netlib.org/fp/ucbtest.tgz [4] http://www.jhauser.us/arithmetic/TestFloat.html [5] http://win-www.uia.ac.be/u/cant/ieeecc754.html