libc/AOR_v20.02/math/v_logf.c

   1 /*
   2  * Single-precision vector log function.
   3  *
   4  * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5  * See https://llvm.org/LICENSE.txt for license information.
   6  * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7  */
   8
   9 #include "mathlib.h"
  10 #include "v_math.h"
  11 #if V_SUPPORTED
  12
  13 static const float Poly[] = {
  14   /* 3.34 ulp error */
  15   -0x1.3e737cp-3f, 0x1.5a9aa2p-3f, -0x1.4f9934p-3f, 0x1.961348p-3f,
  16   -0x1.00187cp-2f, 0x1.555d7cp-2f, -0x1.ffffc8p-2f,
  17 };
  18 #define P7 v_f32 (Poly[0])
  19 #define P6 v_f32 (Poly[1])
  20 #define P5 v_f32 (Poly[2])
  21 #define P4 v_f32 (Poly[3])
  22 #define P3 v_f32 (Poly[4])
  23 #define P2 v_f32 (Poly[5])
  24 #define P1 v_f32 (Poly[6])
  25
  26 #define Ln2 v_f32 (0x1.62e43p-1f) /* 0x3f317218 */
  27 #define Min v_u32 (0x00800000)
  28 #define Max v_u32 (0x7f800000)
  29 #define Mask v_u32 (0x007fffff)
  30 #define Off v_u32 (0x3f2aaaab) /* 0.666667 */
  31
  32 VPCS_ATTR
  33 __attribute__ ((noinline)) static v_f32_t
  34 specialcase (v_f32_t x, v_f32_t y, v_u32_t cmp)
  35 {
  36   /* Fall back to scalar code.  */
  37   return v_call_f32 (logf, x, y, cmp);
  38 }
  39
  40 VPCS_ATTR
  41 v_f32_t
  42 V_NAME(logf) (v_f32_t x)
  43 {
  44   v_f32_t n, p, q, r, r2, y;
  45   v_u32_t u, cmp;
  46
  47   u = v_as_u32_f32 (x);
  48   cmp = v_cond_u32 (u - Min >= Max - Min);
  49
  50   /* x = 2^n * (1+r), where 2/3 < 1+r < 4/3 */
  51   u -= Off;
  52   n = v_to_f32_s32 (v_as_s32_u32 (u) >> 23); /* signextend */
  53   u &= Mask;
  54   u += Off;
  55   r = v_as_f32_u32 (u) - v_f32 (1.0f);
  56
  57   /* y = log(1+r) + n*ln2.  */
  58   r2 = r * r;
  59   /* n*ln2 + r + r2*(P1 + r*P2 + r2*(P3 + r*P4 + r2*(P5 + r*P6 + r2*P7))).  */
  60   p = v_fma_f32 (P6, r, P5);
  61   q = v_fma_f32 (P4, r, P3);
  62   y = v_fma_f32 (P2, r, P1);
  63   p = v_fma_f32 (P7, r2, p);
  64   q = v_fma_f32 (p, r2, q);
  65   y = v_fma_f32 (q, r2, y);
  66   p = v_fma_f32 (Ln2, n, r);
  67   y = v_fma_f32 (y, r2, p);
  68
  69   if (unlikely (v_any_u32 (cmp)))
  70     return specialcase (x, y, cmp);
  71   return y;
  72 }
  73 VPCS_ALIAS
  74 #endif