1 // Copyright 2019 Google LLC
2 //
3 // This source code is licensed under the BSD-style license found in the
4 // LICENSE file in the root directory of this source tree.
5
6 #include <assert.h>
7
8 #include <immintrin.h>
9
10 #include <xnnpack/math-stubs.h>
11
12
xnn_math_f32_exp__avx512f_p5_scalef(size_t n,const float * input,float * output)13 void xnn_math_f32_exp__avx512f_p5_scalef(
14 size_t n,
15 const float* input,
16 float* output)
17 {
18 assert(n % (16 * sizeof(float)) == 0);
19
20 const __m512 vlog2e = _mm512_set1_ps(0x1.715476p+0f);
21 const __m512 vminus_ln2_hi = _mm512_set1_ps(-0x1.62E43p-1f);
22 const __m512 vminus_ln2_lo = _mm512_set1_ps(0x1.05C61p-29f);
23
24 const __m512 vc0 = _mm512_set1_ps(1.0f);
25 const __m512 vc1 = _mm512_set1_ps(0x1.FFFFF6p-1f);
26 const __m512 vc2 = _mm512_set1_ps(0x1.FFFDC6p-2f);
27 const __m512 vc3 = _mm512_set1_ps(0x1.555A80p-3f);
28 const __m512 vc4 = _mm512_set1_ps(0x1.573A1Ap-5f);
29 const __m512 vc5 = _mm512_set1_ps(0x1.0F9F9Cp-7f);
30
31 for (; n != 0; n -= 16 * sizeof(float)) {
32 const __m512 vx = _mm512_loadu_ps(input);
33
34 // Compute reduced argument n := round(x / log(2)).
35 const __m512 vn = _mm512_roundscale_ps(_mm512_mul_ps(vx, vlog2e), 0);
36 // Compute reduced argument t := x - n * log(2).
37 // Use Cody-Waite range reduction method (note two constants to represent log(2)) to improve accuracy.
38 __m512 vt = _mm512_fmadd_ps(vn, vminus_ln2_hi, vx);
39 vt = _mm512_fmadd_ps(vn, vminus_ln2_lo, vt);
40
41 // Compute degree-5 polynomial approxiatmion for exp(t) on [-log(2)/2, log(2)/2].
42 __m512 vp = _mm512_fmadd_ps(vc5, vt, vc4);
43 vp = _mm512_fmadd_ps(vp, vt, vc3);
44 vp = _mm512_fmadd_ps(vp, vt, vc2);
45 vp = _mm512_fmadd_ps(vp, vt, vc1);
46 vp = _mm512_fmadd_ps(vp, vt, vc0);
47
48 // Reconstruct the final value as f = exp2(n) * p.
49 const __m512 vf = _mm512_scalef_ps(vp, vn);
50 _mm512_storeu_ps(output, vf);
51
52 input += 16;
53 output += 16;
54 }
55 }
56