xref: /aosp_15_r20/external/llvm-libc/src/math/generic/exp10f16.cpp (revision 71db0c75aadcf003ffe3238005f61d7618a3fead)
1*71db0c75SAndroid Build Coastguard Worker //===-- Half-precision 10^x function --------------------------------------===//
2*71db0c75SAndroid Build Coastguard Worker //
3*71db0c75SAndroid Build Coastguard Worker // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4*71db0c75SAndroid Build Coastguard Worker // See https://llvm.org/LICENSE.txt for license information.
5*71db0c75SAndroid Build Coastguard Worker // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6*71db0c75SAndroid Build Coastguard Worker //
7*71db0c75SAndroid Build Coastguard Worker //===----------------------------------------------------------------------===//
8*71db0c75SAndroid Build Coastguard Worker 
9*71db0c75SAndroid Build Coastguard Worker #include "src/math/exp10f16.h"
10*71db0c75SAndroid Build Coastguard Worker #include "expxf16.h"
11*71db0c75SAndroid Build Coastguard Worker #include "hdr/errno_macros.h"
12*71db0c75SAndroid Build Coastguard Worker #include "hdr/fenv_macros.h"
13*71db0c75SAndroid Build Coastguard Worker #include "src/__support/CPP/array.h"
14*71db0c75SAndroid Build Coastguard Worker #include "src/__support/FPUtil/FEnvImpl.h"
15*71db0c75SAndroid Build Coastguard Worker #include "src/__support/FPUtil/FPBits.h"
16*71db0c75SAndroid Build Coastguard Worker #include "src/__support/FPUtil/PolyEval.h"
17*71db0c75SAndroid Build Coastguard Worker #include "src/__support/FPUtil/cast.h"
18*71db0c75SAndroid Build Coastguard Worker #include "src/__support/FPUtil/except_value_utils.h"
19*71db0c75SAndroid Build Coastguard Worker #include "src/__support/FPUtil/multiply_add.h"
20*71db0c75SAndroid Build Coastguard Worker #include "src/__support/FPUtil/nearest_integer.h"
21*71db0c75SAndroid Build Coastguard Worker #include "src/__support/FPUtil/rounding_mode.h"
22*71db0c75SAndroid Build Coastguard Worker #include "src/__support/common.h"
23*71db0c75SAndroid Build Coastguard Worker #include "src/__support/macros/config.h"
24*71db0c75SAndroid Build Coastguard Worker #include "src/__support/macros/optimization.h"
25*71db0c75SAndroid Build Coastguard Worker #include "src/__support/macros/properties/cpu_features.h"
26*71db0c75SAndroid Build Coastguard Worker 
27*71db0c75SAndroid Build Coastguard Worker namespace LIBC_NAMESPACE_DECL {
28*71db0c75SAndroid Build Coastguard Worker 
29*71db0c75SAndroid Build Coastguard Worker #ifdef LIBC_TARGET_CPU_HAS_FMA
30*71db0c75SAndroid Build Coastguard Worker static constexpr size_t N_EXP10F16_EXCEPTS = 5;
31*71db0c75SAndroid Build Coastguard Worker #else
32*71db0c75SAndroid Build Coastguard Worker static constexpr size_t N_EXP10F16_EXCEPTS = 8;
33*71db0c75SAndroid Build Coastguard Worker #endif
34*71db0c75SAndroid Build Coastguard Worker 
35*71db0c75SAndroid Build Coastguard Worker static constexpr fputil::ExceptValues<float16, N_EXP10F16_EXCEPTS>
36*71db0c75SAndroid Build Coastguard Worker     EXP10F16_EXCEPTS = {{
37*71db0c75SAndroid Build Coastguard Worker         // x = 0x1.8f4p-2, exp10f16(x) = 0x1.3ap+1 (RZ)
38*71db0c75SAndroid Build Coastguard Worker         {0x363dU, 0x40e8U, 1U, 0U, 1U},
39*71db0c75SAndroid Build Coastguard Worker         // x = 0x1.95cp-2, exp10f16(x) = 0x1.3ecp+1 (RZ)
40*71db0c75SAndroid Build Coastguard Worker         {0x3657U, 0x40fbU, 1U, 0U, 0U},
41*71db0c75SAndroid Build Coastguard Worker         // x = -0x1.018p-4, exp10f16(x) = 0x1.bbp-1 (RZ)
42*71db0c75SAndroid Build Coastguard Worker         {0xac06U, 0x3aecU, 1U, 0U, 0U},
43*71db0c75SAndroid Build Coastguard Worker         // x = -0x1.c28p+0, exp10f16(x) = 0x1.1ccp-6 (RZ)
44*71db0c75SAndroid Build Coastguard Worker         {0xbf0aU, 0x2473U, 1U, 0U, 0U},
45*71db0c75SAndroid Build Coastguard Worker         // x = -0x1.e1cp+1, exp10f16(x) = 0x1.694p-13 (RZ)
46*71db0c75SAndroid Build Coastguard Worker         {0xc387U, 0x09a5U, 1U, 0U, 0U},
47*71db0c75SAndroid Build Coastguard Worker #ifndef LIBC_TARGET_CPU_HAS_FMA
48*71db0c75SAndroid Build Coastguard Worker         // x = 0x1.0cp+1, exp10f16(x) = 0x1.f04p+6 (RZ)
49*71db0c75SAndroid Build Coastguard Worker         {0x4030U, 0x57c1U, 1U, 0U, 1U},
50*71db0c75SAndroid Build Coastguard Worker         // x = 0x1.1b8p+1, exp10f16(x) = 0x1.47cp+7 (RZ)
51*71db0c75SAndroid Build Coastguard Worker         {0x406eU, 0x591fU, 1U, 0U, 1U},
52*71db0c75SAndroid Build Coastguard Worker         // x = 0x1.1b8p+2, exp10f16(x) = 0x1.a4p+14 (RZ)
53*71db0c75SAndroid Build Coastguard Worker         {0x446eU, 0x7690U, 1U, 0U, 1U},
54*71db0c75SAndroid Build Coastguard Worker #endif
55*71db0c75SAndroid Build Coastguard Worker     }};
56*71db0c75SAndroid Build Coastguard Worker 
57*71db0c75SAndroid Build Coastguard Worker LLVM_LIBC_FUNCTION(float16, exp10f16, (float16 x)) {
58*71db0c75SAndroid Build Coastguard Worker   using FPBits = fputil::FPBits<float16>;
59*71db0c75SAndroid Build Coastguard Worker   FPBits x_bits(x);
60*71db0c75SAndroid Build Coastguard Worker 
61*71db0c75SAndroid Build Coastguard Worker   uint16_t x_u = x_bits.uintval();
62*71db0c75SAndroid Build Coastguard Worker   uint16_t x_abs = x_u & 0x7fffU;
63*71db0c75SAndroid Build Coastguard Worker 
64*71db0c75SAndroid Build Coastguard Worker   // When |x| >= 5, or x is NaN.
65*71db0c75SAndroid Build Coastguard Worker   if (LIBC_UNLIKELY(x_abs >= 0x4500U)) {
66*71db0c75SAndroid Build Coastguard Worker     // exp10(NaN) = NaN
67*71db0c75SAndroid Build Coastguard Worker     if (x_bits.is_nan()) {
68*71db0c75SAndroid Build Coastguard Worker       if (x_bits.is_signaling_nan()) {
69*71db0c75SAndroid Build Coastguard Worker         fputil::raise_except_if_required(FE_INVALID);
70*71db0c75SAndroid Build Coastguard Worker         return FPBits::quiet_nan().get_val();
71*71db0c75SAndroid Build Coastguard Worker       }
72*71db0c75SAndroid Build Coastguard Worker 
73*71db0c75SAndroid Build Coastguard Worker       return x;
74*71db0c75SAndroid Build Coastguard Worker     }
75*71db0c75SAndroid Build Coastguard Worker 
76*71db0c75SAndroid Build Coastguard Worker     // When x >= 5.
77*71db0c75SAndroid Build Coastguard Worker     if (x_bits.is_pos()) {
78*71db0c75SAndroid Build Coastguard Worker       // exp10(+inf) = +inf
79*71db0c75SAndroid Build Coastguard Worker       if (x_bits.is_inf())
80*71db0c75SAndroid Build Coastguard Worker         return FPBits::inf().get_val();
81*71db0c75SAndroid Build Coastguard Worker 
82*71db0c75SAndroid Build Coastguard Worker       switch (fputil::quick_get_round()) {
83*71db0c75SAndroid Build Coastguard Worker       case FE_TONEAREST:
84*71db0c75SAndroid Build Coastguard Worker       case FE_UPWARD:
85*71db0c75SAndroid Build Coastguard Worker         fputil::set_errno_if_required(ERANGE);
86*71db0c75SAndroid Build Coastguard Worker         fputil::raise_except_if_required(FE_OVERFLOW);
87*71db0c75SAndroid Build Coastguard Worker         return FPBits::inf().get_val();
88*71db0c75SAndroid Build Coastguard Worker       default:
89*71db0c75SAndroid Build Coastguard Worker         return FPBits::max_normal().get_val();
90*71db0c75SAndroid Build Coastguard Worker       }
91*71db0c75SAndroid Build Coastguard Worker     }
92*71db0c75SAndroid Build Coastguard Worker 
93*71db0c75SAndroid Build Coastguard Worker     // When x <= -8.
94*71db0c75SAndroid Build Coastguard Worker     if (x_u >= 0xc800U) {
95*71db0c75SAndroid Build Coastguard Worker       // exp10(-inf) = +0
96*71db0c75SAndroid Build Coastguard Worker       if (x_bits.is_inf())
97*71db0c75SAndroid Build Coastguard Worker         return FPBits::zero().get_val();
98*71db0c75SAndroid Build Coastguard Worker 
99*71db0c75SAndroid Build Coastguard Worker       fputil::set_errno_if_required(ERANGE);
100*71db0c75SAndroid Build Coastguard Worker       fputil::raise_except_if_required(FE_UNDERFLOW | FE_INEXACT);
101*71db0c75SAndroid Build Coastguard Worker 
102*71db0c75SAndroid Build Coastguard Worker       if (fputil::fenv_is_round_up())
103*71db0c75SAndroid Build Coastguard Worker         return FPBits::min_subnormal().get_val();
104*71db0c75SAndroid Build Coastguard Worker       return FPBits::zero().get_val();
105*71db0c75SAndroid Build Coastguard Worker     }
106*71db0c75SAndroid Build Coastguard Worker   }
107*71db0c75SAndroid Build Coastguard Worker 
108*71db0c75SAndroid Build Coastguard Worker   // When x is 1, 2, 3, or 4. These are hard-to-round cases with exact results.
109*71db0c75SAndroid Build Coastguard Worker   if (LIBC_UNLIKELY((x_u & ~(0x3c00U | 0x4000U | 0x4200U | 0x4400U)) == 0)) {
110*71db0c75SAndroid Build Coastguard Worker     switch (x_u) {
111*71db0c75SAndroid Build Coastguard Worker     case 0x3c00U: // x = 1.0f16
112*71db0c75SAndroid Build Coastguard Worker       return fputil::cast<float16>(10.0);
113*71db0c75SAndroid Build Coastguard Worker     case 0x4000U: // x = 2.0f16
114*71db0c75SAndroid Build Coastguard Worker       return fputil::cast<float16>(100.0);
115*71db0c75SAndroid Build Coastguard Worker     case 0x4200U: // x = 3.0f16
116*71db0c75SAndroid Build Coastguard Worker       return fputil::cast<float16>(1'000.0);
117*71db0c75SAndroid Build Coastguard Worker     case 0x4400U: // x = 4.0f16
118*71db0c75SAndroid Build Coastguard Worker       return fputil::cast<float16>(10'000.0);
119*71db0c75SAndroid Build Coastguard Worker     }
120*71db0c75SAndroid Build Coastguard Worker   }
121*71db0c75SAndroid Build Coastguard Worker 
122*71db0c75SAndroid Build Coastguard Worker   if (auto r = EXP10F16_EXCEPTS.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
123*71db0c75SAndroid Build Coastguard Worker     return r.value();
124*71db0c75SAndroid Build Coastguard Worker 
125*71db0c75SAndroid Build Coastguard Worker   // 10^x = 2^((hi + mid) * log2(10)) * 10^lo
126*71db0c75SAndroid Build Coastguard Worker   auto [exp2_hi_mid, exp10_lo] = exp10_range_reduction(x);
127*71db0c75SAndroid Build Coastguard Worker   return fputil::cast<float16>(exp2_hi_mid * exp10_lo);
128*71db0c75SAndroid Build Coastguard Worker }
129*71db0c75SAndroid Build Coastguard Worker 
130*71db0c75SAndroid Build Coastguard Worker } // namespace LIBC_NAMESPACE_DECL
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