From cf9cf33199fdd6550920ad43f19ad8b2435fc0c6 Mon Sep 17 00:00:00 2001 From: Adhemerval Zanella Netto Date: Mon, 20 Mar 2023 13:01:17 -0300 Subject: math: Improve fmodf This uses a new algorithm similar to already proposed earlier [1]. With x = mx * 2^ex and y = my * 2^ey (mx, my, ex, ey being integers), the simplest implementation is: mx * 2^ex == 2 * mx * 2^(ex - 1) while (ex > ey) { mx *= 2; --ex; mx %= my; } With mx/my being mantissa of double floating pointer, on each step the argument reduction can be improved 8 (which is sizeof of uint32_t minus MANTISSA_WIDTH plus the signal bit): while (ex > ey) { mx << 8; ex -= 8; mx %= my; } */ The implementation uses builtin clz and ctz, along with shifts to convert hx/hy back to doubles. Different than the original patch, this path assume modulo/divide operation is slow, so use multiplication with invert values. I see the following performance improvements using fmod benchtests (result only show the 'mean' result): Architecture | Input | master | patch -----------------|-----------------|----------|-------- x86_64 (Ryzen 9) | subnormals | 17.2549 | 12.0318 x86_64 (Ryzen 9) | normal | 85.4096 | 49.9641 x86_64 (Ryzen 9) | close-exponents | 19.1072 | 15.8224 aarch64 (N1) | subnormal | 10.2182 | 6.81778 aarch64 (N1) | normal | 60.0616 | 20.3667 aarch64 (N1) | close-exponents | 11.5256 | 8.39685 I also see similar improvements on arm-linux-gnueabihf when running on the N1 aarch64 chips, where it a lot of soft-fp implementation (for modulo, and multiplication): Architecture | Input | master | patch -----------------|-----------------|----------|-------- armhf (N1) | subnormal | 11.6662 | 10.8955 armhf (N1) | normal | 69.2759 | 34.1524 armhf (N1) | close-exponents | 13.6472 | 18.2131 Instead of using the math_private.h definitions, I used the math_config.h instead which is used on newer math implementations. Co-authored-by: kirill [1] https://sourceware.org/pipermail/libc-alpha/2020-November/119794.html Reviewed-by: Wilco Dijkstra --- math/libm-test-fmod.inc | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'math') diff --git a/math/libm-test-fmod.inc b/math/libm-test-fmod.inc index 8841c1332c..43376c3df2 100644 --- a/math/libm-test-fmod.inc +++ b/math/libm-test-fmod.inc @@ -213,6 +213,10 @@ static const struct test_ff_f_data fmod_test_data[] = TEST_ff_f (fmod, -0x1p127L, -0x3p-148L, -0x1p-147L, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED), TEST_ff_f (fmod, -0x1p127L, 0x3p-126L, -0x1p-125L, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED), TEST_ff_f (fmod, -0x1p127L, -0x3p-126L, -0x1p-125L, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED), + TEST_ff_f (fmod, 0x1.3a3e6p-127, 0x1.8b8338p-128, 0x1.d1f31p-129, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED), + TEST_ff_f (fmod, 0x1.3a3e6p-127, -0x1.8b8338p-128, 0x1.d1f31p-129, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED), + TEST_ff_f (fmod, -0x1.3a3e6p-127, 0x1.8b8338p-128, -0x1.d1f31p-129, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED), + TEST_ff_f (fmod, -0x1.3a3e6p-127, -0x1.8b8338p-128, -0x1.d1f31p-129, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED), #if !TEST_COND_binary32 TEST_ff_f (fmod, 0x1p1023L, 0x3p-1074L, 0x1p-1073L, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED), TEST_ff_f (fmod, 0x1p1023L, -0x3p-1074L, 0x1p-1073L, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED), -- cgit 1.4.1