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Diffstat (limited to 'pl/math/sv_asin_3u.c')
| -rw-r--r-- | pl/math/sv_asin_3u.c | 84 |
1 files changed, 84 insertions, 0 deletions
diff --git a/pl/math/sv_asin_3u.c b/pl/math/sv_asin_3u.c new file mode 100644 index 000000000000..c3dd37b145ae --- /dev/null +++ b/pl/math/sv_asin_3u.c @@ -0,0 +1,84 @@ +/* + * Double-precision SVE asin(x) function. + * + * Copyright (c) 2023, Arm Limited. + * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception + */ + +#include "sv_math.h" +#include "poly_sve_f64.h" +#include "pl_sig.h" +#include "pl_test.h" + +static const struct data +{ + float64_t poly[12]; + float64_t pi_over_2f; +} data = { + /* Polynomial approximation of (asin(sqrt(x)) - sqrt(x)) / (x * sqrt(x)) + on [ 0x1p-106, 0x1p-2 ], relative error: 0x1.c3d8e169p-57. */ + .poly = { 0x1.555555555554ep-3, 0x1.3333333337233p-4, + 0x1.6db6db67f6d9fp-5, 0x1.f1c71fbd29fbbp-6, + 0x1.6e8b264d467d6p-6, 0x1.1c5997c357e9dp-6, + 0x1.c86a22cd9389dp-7, 0x1.856073c22ebbep-7, + 0x1.fd1151acb6bedp-8, 0x1.087182f799c1dp-6, + -0x1.6602748120927p-7, 0x1.cfa0dd1f9478p-6, }, + .pi_over_2f = 0x1.921fb54442d18p+0, +}; + +#define P(i) sv_f64 (d->poly[i]) + +/* Double-precision SVE implementation of vector asin(x). + + For |x| in [0, 0.5], use an order 11 polynomial P such that the final + approximation is an odd polynomial: asin(x) ~ x + x^3 P(x^2). + + The largest observed error in this region is 0.52 ulps, + _ZGVsMxv_asin(0x1.d95ae04998b6cp-2) got 0x1.ec13757305f27p-2 + want 0x1.ec13757305f26p-2. + + For |x| in [0.5, 1.0], use same approximation with a change of variable + + asin(x) = pi/2 - (y + y * z * P(z)), with z = (1-x)/2 and y = sqrt(z). + + The largest observed error in this region is 2.69 ulps, + _ZGVsMxv_asin(0x1.044ac9819f573p-1) got 0x1.110d7e85fdd5p-1 + want 0x1.110d7e85fdd53p-1. */ +svfloat64_t SV_NAME_D1 (asin) (svfloat64_t x, const svbool_t pg) +{ + const struct data *d = ptr_barrier (&data); + + svuint64_t sign = svand_x (pg, svreinterpret_u64 (x), 0x8000000000000000); + svfloat64_t ax = svabs_x (pg, x); + svbool_t a_ge_half = svacge (pg, x, 0.5); + + /* Evaluate polynomial Q(x) = y + y * z * P(z) with + z = x ^ 2 and y = |x| , if |x| < 0.5 + z = (1 - |x|) / 2 and y = sqrt(z), if |x| >= 0.5. */ + svfloat64_t z2 = svsel (a_ge_half, svmls_x (pg, sv_f64 (0.5), ax, 0.5), + svmul_x (pg, x, x)); + svfloat64_t z = svsqrt_m (ax, a_ge_half, z2); + + /* Use a single polynomial approximation P for both intervals. */ + svfloat64_t z4 = svmul_x (pg, z2, z2); + svfloat64_t z8 = svmul_x (pg, z4, z4); + svfloat64_t z16 = svmul_x (pg, z8, z8); + svfloat64_t p = sv_estrin_11_f64_x (pg, z2, z4, z8, z16, d->poly); + /* Finalize polynomial: z + z * z2 * P(z2). */ + p = svmla_x (pg, z, svmul_x (pg, z, z2), p); + + /* asin(|x|) = Q(|x|) , for |x| < 0.5 + = pi/2 - 2 Q(|x|), for |x| >= 0.5. */ + svfloat64_t y = svmad_m (a_ge_half, p, sv_f64 (-2.0), d->pi_over_2f); + + /* Copy sign. */ + return svreinterpret_f64 (svorr_x (pg, svreinterpret_u64 (y), sign)); +} + +PL_SIG (SV, D, 1, asin, -1.0, 1.0) +PL_TEST_ULP (SV_NAME_D1 (asin), 2.19) +PL_TEST_INTERVAL (SV_NAME_D1 (asin), 0, 0.5, 50000) +PL_TEST_INTERVAL (SV_NAME_D1 (asin), 0.5, 1.0, 50000) +PL_TEST_INTERVAL (SV_NAME_D1 (asin), 1.0, 0x1p11, 50000) +PL_TEST_INTERVAL (SV_NAME_D1 (asin), 0x1p11, inf, 20000) +PL_TEST_INTERVAL (SV_NAME_D1 (asin), -0, -inf, 20000) |