1 /*
2 * Double-precision SVE powi(x, n) function.
3 *
4 * Copyright (c) 2020-2023, Arm Limited.
5 * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception
6 */
7
8 #include "sv_math.h"
9 #if SV_SUPPORTED
10
11 /* Optimized double-precision vector powi (double base, long integer power).
12 powi is developed for environments in which accuracy is of much less
13 importance than performance, hence we provide no estimate for worst-case
14 error. */
15 svfloat64_t
__sv_powi_x(svfloat64_t as,svint64_t ns,svbool_t p)16 __sv_powi_x (svfloat64_t as, svint64_t ns, svbool_t p)
17 {
18 /* Compute powi by successive squaring, right to left. */
19 svfloat64_t acc = svdup_n_f64 (1.0);
20 svbool_t want_recip = svcmplt_n_s64 (p, ns, 0);
21 svuint64_t ns_abs = svreinterpret_u64_s64 (svabs_s64_x (p, ns));
22
23 /* We use a max to avoid needing to check whether any lane != 0 on each
24 iteration. */
25 uint64_t max_n = svmaxv_u64 (p, ns_abs);
26
27 svfloat64_t c = as;
28 /* Successively square c, and use merging predication (_m) to determine
29 whether or not to perform the multiplication or keep the previous
30 iteration. */
31 while (true)
32 {
33 svbool_t px = svcmpeq_n_u64 (p, svand_n_u64_x (p, ns_abs, 1ull), 1ull);
34 acc = svmul_f64_m (px, acc, c);
35 max_n >>= 1;
36 if (max_n == 0)
37 break;
38
39 ns_abs = svlsr_n_u64_x (p, ns_abs, 1);
40 c = svmul_f64_x (p, c, c);
41 }
42
43 /* Negative powers are handled by computing the abs(n) version and then
44 taking the reciprocal. */
45 if (svptest_any (want_recip, want_recip))
46 acc = svdivr_n_f64_m (want_recip, acc, 1.0);
47
48 return acc;
49 }
50
51 strong_alias (__sv_powi_x, _ZGVsMxvv_powk)
52
53 #endif // SV_SUPPORTED
54