diff options
| author | Georg-Johann Lay <avr@gjlay.de> | 2023-11-14 12:05:19 +0100 |
|---|---|---|
| committer | Georg-Johann Lay <avr@gjlay.de> | 2023-11-14 12:10:08 +0100 |
| commit | 3232e73c446a3a70fd2fcce4eabc0564b08312a7 (patch) | |
| tree | 1ca35ea616aa3b029bb1931a4395d639b33cff38 /libgcc/config/avr | |
| parent | e47e836f3138f89350e2fcd42ee1ec6741008bcb (diff) | |
| download | gcc-3232e73c446a3a70fd2fcce4eabc0564b08312a7.zip gcc-3232e73c446a3a70fd2fcce4eabc0564b08312a7.tar.gz gcc-3232e73c446a3a70fd2fcce4eabc0564b08312a7.tar.bz2 | |
LibF7: sinh: Fix loss of precision due to cancellation for small values.
libgcc/config/avr/libf7/
* libf7-const.def [F7MOD_sinh_]: Add MiniMax polynomial.
* libf7.c (f7_sinh): Use it instead of (exp(x) - exp(-x)) / 2
when |x| < 0.5 to avoid loss of precision due to cancellation.
Diffstat (limited to 'libgcc/config/avr')
| -rw-r--r-- | libgcc/config/avr/libf7/libf7-const.def | 10 | ||||
| -rw-r--r-- | libgcc/config/avr/libf7/libf7.c | 17 |
2 files changed, 27 insertions, 0 deletions
diff --git a/libgcc/config/avr/libf7/libf7-const.def b/libgcc/config/avr/libf7/libf7-const.def index 0e4c4d8..f772adb 100644 --- a/libgcc/config/avr/libf7/libf7-const.def +++ b/libgcc/config/avr/libf7/libf7-const.def @@ -194,5 +194,15 @@ F7_CONST_DEF (X, 1, 0xc7,0xb5,0x6a,0xf8,0x0e,0x32,0x07, -37) F7_CONST_DEF (pi_low,0, 0xd3,0x13,0x19,0x8a,0x2e,0x03,0x70, 1 - F7_MANT_BITS-2) #endif +#elif defined (F7MOD_sinh_) +// MiniMax for sinh(q)/q, q = sqrt(x) for q in [0, 0.2505]. Quality pQ10 > 70. +// 0.99999999999999998094379 + 0.16666666666667217765428 x + 0.0083333333330755574996361 x^2 + 1.9841270281701916844502e-4 x^3 + 2.7556979384534689658282e-6 x^4 + 2.5172859336028750964929e-8 x^5 +F7_CONST_DEF (X, 0, 0xff,0xff,0xff,0xff,0xff,0xff,0xff, -1) +F7_CONST_DEF (X, 0, 0xaa,0xaa,0xaa,0xaa,0xaa,0xb0,0xdf, -3) +F7_CONST_DEF (X, 0, 0x88,0x88,0x88,0x88,0x76,0x64,0xdb, -7) +F7_CONST_DEF (X, 0, 0xd0,0x0d,0x01,0x1d,0x88,0x4c,0xed, -13) +F7_CONST_DEF (X, 0, 0xb8,0xee,0x87,0xb4,0x30,0xf0,0xa1, -19) +F7_CONST_DEF (X, 0, 0xd8,0x3b,0xb3,0xfd,0x9e,0x6c,0xcf, -26) + #endif #endif /* ! IN_LIBF7_H && ! F7MOD_const_ */ diff --git a/libgcc/config/avr/libf7/libf7.c b/libgcc/config/avr/libf7/libf7.c index da2a4b6..bf1cd14 100644 --- a/libgcc/config/avr/libf7/libf7.c +++ b/libgcc/config/avr/libf7/libf7.c @@ -2022,9 +2022,26 @@ void f7_sinhcosh (f7_t *cc, const f7_t *aa, bool do_sinh) #ifdef F7MOD_sinh_ + +#define ARRAY_NAME coeff_sinh +#include "libf7-array.def" +#undef ARRAY_NAME + F7_WEAK void f7_sinh (f7_t *cc, const f7_t *aa) { + if (aa->expo <= -2) + { + // For small values, exp(A) - exp(-A) suffers from cancellation, hence + // use a MiniMax polynomial for |A| < 0.5. + f7_t xx7, *xx = &xx7; + f7_t hh7, *hh = &hh7; + f7_square (xx, aa); + f7_horner (hh, xx, n_coeff_sinh, coeff_sinh, NULL); + f7_mul (cc, aa, hh); + return; + } + f7_sinhcosh (cc, aa, true); } #endif // F7MOD_sinh_ |