1 /*
2 * Single-precision SVE tanh(x) function.
3 *
4 * Copyright (c) 2023, Arm Limited.
5 * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception
6 */
7
8 #include "sv_math.h"
9 #include "pl_sig.h"
10 #include "pl_test.h"
11
12 #include "sv_expm1f_inline.h"
13
14 static const struct data
15 {
16 struct sv_expm1f_data expm1f_consts;
17 uint32_t boring_bound, onef;
18 } data = {
19 .expm1f_consts = SV_EXPM1F_DATA,
20 /* 0x1.205966p+3, above which tanhf rounds to 1 (or -1 for negative). */
21 .boring_bound = 0x41102cb3,
22 .onef = 0x3f800000,
23 };
24
25 static svfloat32_t NOINLINE
special_case(svfloat32_t x,svfloat32_t y,svbool_t special)26 special_case (svfloat32_t x, svfloat32_t y, svbool_t special)
27 {
28 return sv_call_f32 (tanhf, x, y, special);
29 }
30
31 /* Approximation for single-precision SVE tanh(x), using a simplified
32 version of expm1f. The maximum error is 2.57 ULP:
33 _ZGVsMxv_tanhf (0x1.fc1832p-5) got 0x1.fb71a4p-5
34 want 0x1.fb71aap-5. */
SV_NAME_F1(tanh)35 svfloat32_t SV_NAME_F1 (tanh) (svfloat32_t x, const svbool_t pg)
36 {
37 const struct data *d = ptr_barrier (&data);
38
39 svfloat32_t ax = svabs_x (pg, x);
40 svuint32_t iax = svreinterpret_u32 (ax);
41 svuint32_t sign = sveor_x (pg, svreinterpret_u32 (x), iax);
42 svbool_t is_boring = svcmpgt (pg, iax, d->boring_bound);
43 svfloat32_t boring = svreinterpret_f32 (svorr_x (pg, sign, d->onef));
44
45 svbool_t special = svcmpgt (pg, iax, 0x7f800000);
46
47 /* tanh(x) = (e^2x - 1) / (e^2x + 1). */
48 svfloat32_t q = expm1f_inline (svmul_x (pg, x, 2.0), pg, &d->expm1f_consts);
49 svfloat32_t y = svdiv_x (pg, q, svadd_x (pg, q, 2.0));
50 if (unlikely (svptest_any (pg, special)))
51 return special_case (x, svsel_f32 (is_boring, boring, y), special);
52 return svsel_f32 (is_boring, boring, y);
53 }
54
55 PL_SIG (SV, F, 1, tanh, -10.0, 10.0)
56 PL_TEST_ULP (SV_NAME_F1 (tanh), 2.07)
57 PL_TEST_SYM_INTERVAL (SV_NAME_F1 (tanh), 0, 0x1p-23, 1000)
58 PL_TEST_SYM_INTERVAL (SV_NAME_F1 (tanh), 0x1p-23, 0x1.205966p+3, 100000)
59 PL_TEST_SYM_INTERVAL (SV_NAME_F1 (tanh), 0x1.205966p+3, inf, 100)
60