1 /*
2 * Single-precision vector log function - inline version
3 *
4 * Copyright (c) 2019-2023, Arm Limited.
5 * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception
6 */
7
8 #include "v_math.h"
9
10 struct v_logf_data
11 {
12 float32x4_t poly[7];
13 float32x4_t ln2;
14 uint32x4_t off, mantissa_mask;
15 };
16
17 #define V_LOGF_CONSTANTS \
18 { \
19 .poly \
20 = { V4 (-0x1.3e737cp-3f), V4 (0x1.5a9aa2p-3f), V4 (-0x1.4f9934p-3f), \
21 V4 (0x1.961348p-3f), V4 (-0x1.00187cp-2f), V4 (0x1.555d7cp-2f), \
22 V4 (-0x1.ffffc8p-2f) }, \
23 .ln2 = V4 (0x1.62e43p-1f), .off = V4 (0x3f2aaaab), \
24 .mantissa_mask = V4 (0x007fffff) \
25 }
26
27 #define P(i) d->poly[7 - i]
28
29 static inline float32x4_t
v_logf_inline(float32x4_t x,const struct v_logf_data * d)30 v_logf_inline (float32x4_t x, const struct v_logf_data *d)
31 {
32 float32x4_t n, p, q, r, r2, y;
33 uint32x4_t u;
34
35 u = vreinterpretq_u32_f32 (x);
36
37 /* x = 2^n * (1+r), where 2/3 < 1+r < 4/3. */
38 u = vsubq_u32 (u, d->off);
39 n = vcvtq_f32_s32 (
40 vshrq_n_s32 (vreinterpretq_s32_u32 (u), 23)); /* signextend. */
41 u = vandq_u32 (u, d->mantissa_mask);
42 u = vaddq_u32 (u, d->off);
43 r = vsubq_f32 (vreinterpretq_f32_u32 (u), v_f32 (1.0f));
44
45 /* y = log(1+r) + n*ln2. */
46 r2 = vmulq_f32 (r, r);
47 /* n*ln2 + r + r2*(P1 + r*P2 + r2*(P3 + r*P4 + r2*(P5 + r*P6 + r2*P7))). */
48 p = vfmaq_f32 (P (5), P (6), r);
49 q = vfmaq_f32 (P (3), P (4), r);
50 y = vfmaq_f32 (P (1), P (2), r);
51 p = vfmaq_f32 (p, P (7), r2);
52 q = vfmaq_f32 (q, p, r2);
53 y = vfmaq_f32 (y, q, r2);
54 p = vfmaq_f32 (r, d->ln2, n);
55
56 return vfmaq_f32 (p, y, r2);
57 }
58
59 #undef P
60