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overmightyovermighty
authoredNov 7, 2024··
[libc][math][c23] Add exp10m1f C23 math function (#87992)
Fixes #86503.
·
llvmorg-21-initllvmorg-20.1.0-rc1
1 parent 49ee606 commit faefedf

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-8
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16 files changed

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‎libc/config/linux/x86_64/entrypoints.txt

+1
Original file line numberDiff line numberDiff line change
@@ -417,6 +417,7 @@ set(TARGET_LIBM_ENTRYPOINTS
417417
libc.src.math.exp
418418
libc.src.math.exp10
419419
libc.src.math.exp10f
420+
libc.src.math.exp10m1f
420421
libc.src.math.exp2
421422
libc.src.math.exp2f
422423
libc.src.math.exp2m1f

‎libc/docs/math/index.rst

+1-1
Original file line numberDiff line numberDiff line change
@@ -292,7 +292,7 @@ Higher Math Functions
292292
+-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
293293
| exp10 | |check| | |check| | | |check| | | 7.12.6.2 | F.10.3.2 |
294294
+-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
295-
| exp10m1 | | | | |check| | | 7.12.6.3 | F.10.3.3 |
295+
| exp10m1 | |check| | | | |check| | | 7.12.6.3 | F.10.3.3 |
296296
+-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
297297
| exp2 | |check| | |check| | | |check| | | 7.12.6.4 | F.10.3.4 |
298298
+-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+

‎libc/newhdrgen/yaml/math.yaml

+6
Original file line numberDiff line numberDiff line change
@@ -280,6 +280,12 @@ functions:
280280
return_type: float
281281
arguments:
282282
- type: float
283+
- name: exp10m1f
284+
standards:
285+
- stdc
286+
return_type: float
287+
arguments:
288+
- type: float
283289
- name: exp10m1f16
284290
standards:
285291
- stdc

‎libc/spec/stdc.td

+1-1
Original file line numberDiff line numberDiff line change
@@ -695,6 +695,7 @@ def StdC : StandardSpec<"stdc"> {
695695
FunctionSpec<"exp10f", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,
696696
GuardedFunctionSpec<"exp10f16", RetValSpec<Float16Type>, [ArgSpec<Float16Type>], "LIBC_TYPES_HAS_FLOAT16">,
697697

698+
FunctionSpec<"exp10m1f", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,
698699
GuardedFunctionSpec<"exp10m1f16", RetValSpec<Float16Type>, [ArgSpec<Float16Type>], "LIBC_TYPES_HAS_FLOAT16">,
699700

700701
FunctionSpec<"remainder", RetValSpec<DoubleType>, [ArgSpec<DoubleType>, ArgSpec<DoubleType>]>,
@@ -1737,7 +1738,6 @@ def StdC : StandardSpec<"stdc"> {
17371738
]
17381739
>;
17391740

1740-
17411741
NamedType StructLconv = NamedType<"struct lconv">;
17421742
PtrType StructLconvPtr = PtrType<StructLconv>;
17431743

‎libc/src/math/CMakeLists.txt

+1
Original file line numberDiff line numberDiff line change
@@ -131,6 +131,7 @@ add_math_entrypoint_object(exp10)
131131
add_math_entrypoint_object(exp10f)
132132
add_math_entrypoint_object(exp10f16)
133133

134+
add_math_entrypoint_object(exp10m1f)
134135
add_math_entrypoint_object(exp10m1f16)
135136

136137
add_math_entrypoint_object(expm1)

‎libc/src/math/exp10m1f.h

+20
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,20 @@
1+
//===-- Implementation header for exp10m1f ----------------------*- C++ -*-===//
2+
//
3+
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4+
// See https://llvm.org/LICENSE.txt for license information.
5+
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6+
//
7+
//===----------------------------------------------------------------------===//
8+
9+
#ifndef LLVM_LIBC_SRC_MATH_EXP10M1F_H
10+
#define LLVM_LIBC_SRC_MATH_EXP10M1F_H
11+
12+
#include "src/__support/macros/config.h"
13+
14+
namespace LIBC_NAMESPACE_DECL {
15+
16+
float exp10m1f(float x);
17+
18+
} // namespace LIBC_NAMESPACE_DECL
19+
20+
#endif // LLVM_LIBC_SRC_MATH_EXP10M1F_H

‎libc/src/math/generic/CMakeLists.txt

+23-1
Original file line numberDiff line numberDiff line change
@@ -359,7 +359,7 @@ add_header_library(
359359
libc.src.__support.FPUtil.fp_bits
360360
libc.src.__support.FPUtil.polyeval
361361
libc.src.__support.FPUtil.nearest_integer
362-
libc.src.__support.common
362+
libc.src.__support.common
363363
)
364364

365365
add_header_library(
@@ -1569,6 +1569,7 @@ add_entrypoint_object(
15691569
.explogxf
15701570
libc.src.errno.errno
15711571
libc.src.__support.common
1572+
libc.src.__support.FPUtil.except_value_utils
15721573
libc.src.__support.FPUtil.fenv_impl
15731574
libc.src.__support.FPUtil.fp_bits
15741575
libc.src.__support.FPUtil.multiply_add
@@ -1686,6 +1687,27 @@ add_entrypoint_object(
16861687
-O3
16871688
)
16881689

1690+
add_entrypoint_object(
1691+
exp10m1f
1692+
SRCS
1693+
exp10m1f.cpp
1694+
HDRS
1695+
../exp10m1f.h
1696+
DEPENDS
1697+
.explogxf
1698+
libc.src.errno.errno
1699+
libc.src.__support.common
1700+
libc.src.__support.FPUtil.except_value_utils
1701+
libc.src.__support.FPUtil.fenv_impl
1702+
libc.src.__support.FPUtil.fp_bits
1703+
libc.src.__support.FPUtil.multiply_add
1704+
libc.src.__support.FPUtil.polyeval
1705+
libc.src.__support.FPUtil.rounding_mode
1706+
libc.src.__support.macros.optimization
1707+
COMPILE_OPTIONS
1708+
-O3
1709+
)
1710+
16891711
add_entrypoint_object(
16901712
exp10m1f16
16911713
SRCS

‎libc/src/math/generic/exp10m1f.cpp

+216
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,216 @@
1+
//===-- Implementation of exp10m1f function -------------------------------===//
2+
//
3+
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4+
// See https://llvm.org/LICENSE.txt for license information.
5+
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6+
//
7+
//===----------------------------------------------------------------------===//
8+
9+
#include "src/math/exp10m1f.h"
10+
#include "src/__support/FPUtil/FEnvImpl.h"
11+
#include "src/__support/FPUtil/FPBits.h"
12+
#include "src/__support/FPUtil/PolyEval.h"
13+
#include "src/__support/FPUtil/except_value_utils.h"
14+
#include "src/__support/FPUtil/multiply_add.h"
15+
#include "src/__support/FPUtil/rounding_mode.h"
16+
#include "src/__support/common.h"
17+
#include "src/__support/macros/config.h"
18+
#include "src/__support/macros/optimization.h"
19+
#include "src/errno/libc_errno.h"
20+
21+
#include "explogxf.h"
22+
23+
namespace LIBC_NAMESPACE_DECL {
24+
25+
static constexpr size_t N_EXCEPTS_LO = 11;
26+
27+
static constexpr fputil::ExceptValues<float, N_EXCEPTS_LO> EXP10M1F_EXCEPTS_LO =
28+
{{
29+
// x = 0x1.0fe54ep-11, exp10m1f(x) = 0x1.3937eep-10 (RZ)
30+
{0x3a07'f2a7U, 0x3a9c'9bf7U, 1U, 0U, 1U},
31+
// x = 0x1.80e6eap-11, exp10m1f(x) = 0x1.bb8272p-10 (RZ)
32+
{0x3a40'7375U, 0x3add'c139U, 1U, 0U, 1U},
33+
// x = -0x1.2a33bcp-51, exp10m1f(x) = -0x1.57515ep-50 (RZ)
34+
{0xa615'19deU, 0xa6ab'a8afU, 0U, 1U, 0U},
35+
// x = -0x0p+0, exp10m1f(x) = -0x0p+0 (RZ)
36+
{0x8000'0000U, 0x8000'0000U, 0U, 0U, 0U},
37+
// x = -0x1.b59e08p-31, exp10m1f(x) = -0x1.f7d356p-30 (RZ)
38+
{0xb05a'cf04U, 0xb0fb'e9abU, 0U, 1U, 1U},
39+
// x = -0x1.bf342p-12, exp10m1f(x) = -0x1.014e02p-10 (RZ)
40+
{0xb9df'9a10U, 0xba80'a701U, 0U, 1U, 0U},
41+
// x = -0x1.6207fp-11, exp10m1f(x) = -0x1.9746cap-10 (RZ)
42+
{0xba31'03f8U, 0xbacb'a365U, 0U, 1U, 1U},
43+
// x = -0x1.bd0c66p-11, exp10m1f(x) = -0x1.ffe168p-10 (RZ)
44+
{0xba5e'8633U, 0xbaff'f0b4U, 0U, 1U, 1U},
45+
// x = -0x1.ffd84cp-10, exp10m1f(x) = -0x1.25faf2p-8 (RZ)
46+
{0xbaff'ec26U, 0xbb92'fd79U, 0U, 1U, 0U},
47+
// x = -0x1.a74172p-9, exp10m1f(x) = -0x1.e57be2p-8 (RZ)
48+
{0xbb53'a0b9U, 0xbbf2'bdf1U, 0U, 1U, 1U},
49+
// x = -0x1.cb694cp-9, exp10m1f(x) = -0x1.0764e4p-7 (RZ)
50+
{0xbb65'b4a6U, 0xbc03'b272U, 0U, 1U, 0U},
51+
}};
52+
53+
static constexpr size_t N_EXCEPTS_HI = 19;
54+
55+
static constexpr fputil::ExceptValues<float, N_EXCEPTS_HI> EXP10M1F_EXCEPTS_HI =
56+
{{
57+
// (input, RZ output, RU offset, RD offset, RN offset)
58+
// x = 0x1.8d31eep-8, exp10m1f(x) = 0x1.cc7e4cp-7 (RZ)
59+
{0x3bc6'98f7U, 0x3c66'3f26U, 1U, 0U, 1U},
60+
// x = 0x1.915fcep-8, exp10m1f(x) = 0x1.d15f72p-7 (RZ)
61+
{0x3bc8'afe7U, 0x3c68'afb9U, 1U, 0U, 0U},
62+
// x = 0x1.bcf982p-8, exp10m1f(x) = 0x1.022928p-6 (RZ)
63+
{0x3bde'7cc1U, 0x3c81'1494U, 1U, 0U, 1U},
64+
// x = 0x1.99ff0ap-7, exp10m1f(x) = 0x1.dee416p-6 (RZ)
65+
{0x3c4c'ff85U, 0x3cef'720bU, 1U, 0U, 0U},
66+
// x = 0x1.75ea14p-6, exp10m1f(x) = 0x1.b9ff16p-5 (RZ)
67+
{0x3cba'f50aU, 0x3d5c'ff8bU, 1U, 0U, 0U},
68+
// x = 0x1.f81b64p-6, exp10m1f(x) = 0x1.2cb6bcp-4 (RZ)
69+
{0x3cfc'0db2U, 0x3d96'5b5eU, 1U, 0U, 0U},
70+
// x = 0x1.fafecp+3, exp10m1f(x) = 0x1.8c880ap+52 (RZ)
71+
{0x417d'7f60U, 0x59c6'4405U, 1U, 0U, 0U},
72+
// x = -0x1.3bf094p-8, exp10m1f(x) = -0x1.69ba4ap-7 (RZ)
73+
{0xbb9d'f84aU, 0xbc34'dd25U, 0U, 1U, 0U},
74+
// x = -0x1.4558bcp-8, exp10m1f(x) = -0x1.746fb8p-7 (RZ)
75+
{0xbba2'ac5eU, 0xbc3a'37dcU, 0U, 1U, 1U},
76+
// x = -0x1.4bb43p-8, exp10m1f(x) = -0x1.7babe4p-7 (RZ)
77+
{0xbba5'da18U, 0xbc3d'd5f2U, 0U, 1U, 1U},
78+
// x = -0x1.776cc8p-8, exp10m1f(x) = -0x1.ad62c4p-7 (RZ)
79+
{0xbbbb'b664U, 0xbc56'b162U, 0U, 1U, 0U},
80+
// x = -0x1.f024cp-8, exp10m1f(x) = -0x1.1b20d6p-6 (RZ)
81+
{0xbbf8'1260U, 0xbc8d'906bU, 0U, 1U, 1U},
82+
// x = -0x1.f510eep-8, exp10m1f(x) = -0x1.1de9aap-6 (RZ)
83+
{0xbbfa'8877U, 0xbc8e'f4d5U, 0U, 1U, 0U},
84+
// x = -0x1.0b43c4p-7, exp10m1f(x) = -0x1.30d418p-6 (RZ)
85+
{0xbc05'a1e2U, 0xbc98'6a0cU, 0U, 1U, 0U},
86+
// x = -0x1.245ee4p-7, exp10m1f(x) = -0x1.4d2b86p-6 (RZ)
87+
{0xbc12'2f72U, 0xbca6'95c3U, 0U, 1U, 0U},
88+
// x = -0x1.f9f2dap-7, exp10m1f(x) = -0x1.1e2186p-5 (RZ)
89+
{0xbc7c'f96dU, 0xbd0f'10c3U, 0U, 1U, 0U},
90+
// x = -0x1.08e42p-6, exp10m1f(x) = -0x1.2b5c4p-5 (RZ)
91+
{0xbc84'7210U, 0xbd15'ae20U, 0U, 1U, 1U},
92+
// x = -0x1.0cdc44p-5, exp10m1f(x) = -0x1.2a2152p-4 (RZ)
93+
{0xbd06'6e22U, 0xbd95'10a9U, 0U, 1U, 1U},
94+
// x = -0x1.ca4322p-5, exp10m1f(x) = -0x1.ef073p-4 (RZ)
95+
{0xbd65'2191U, 0xbdf7'8398U, 0U, 1U, 1U},
96+
}};
97+
98+
LLVM_LIBC_FUNCTION(float, exp10m1f, (float x)) {
99+
using FPBits = fputil::FPBits<float>;
100+
FPBits xbits(x);
101+
102+
uint32_t x_u = xbits.uintval();
103+
uint32_t x_abs = x_u & 0x7fff'ffffU;
104+
105+
// When x >= log10(2^128), or x is nan
106+
if (LIBC_UNLIKELY(xbits.is_pos() && x_u >= 0x421a'209bU)) {
107+
if (xbits.is_finite()) {
108+
int rounding = fputil::quick_get_round();
109+
if (rounding == FE_DOWNWARD || rounding == FE_TOWARDZERO)
110+
return FPBits::max_normal().get_val();
111+
112+
fputil::set_errno_if_required(ERANGE);
113+
fputil::raise_except_if_required(FE_OVERFLOW);
114+
}
115+
116+
// x >= log10(2^128) and 10^x - 1 rounds to +inf, or x is +inf or nan
117+
return x + FPBits::inf().get_val();
118+
}
119+
120+
// When |x| <= log10(2) * 2^(-6)
121+
if (LIBC_UNLIKELY(x_abs <= 0x3b9a'209bU)) {
122+
if (auto r = EXP10M1F_EXCEPTS_LO.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
123+
return r.value();
124+
125+
double dx = x;
126+
double dx_sq = dx * dx;
127+
double c0 = dx * Exp10Base::COEFFS[0];
128+
double c1 =
129+
fputil::multiply_add(dx, Exp10Base::COEFFS[2], Exp10Base::COEFFS[1]);
130+
double c2 =
131+
fputil::multiply_add(dx, Exp10Base::COEFFS[4], Exp10Base::COEFFS[3]);
132+
// 10^dx - 1 ~ (1 + COEFFS[0] * dx + ... + COEFFS[4] * dx^5) - 1
133+
// = COEFFS[0] * dx + ... + COEFFS[4] * dx^5
134+
return static_cast<float>(fputil::polyeval(dx_sq, c0, c1, c2));
135+
}
136+
137+
// When x <= log10(2^-25), or x is nan
138+
if (LIBC_UNLIKELY(x_u >= 0xc0f0d2f1)) {
139+
// exp10m1(-inf) = -1
140+
if (xbits.is_inf())
141+
return -1.0f;
142+
// exp10m1(nan) = nan
143+
if (xbits.is_nan())
144+
return x;
145+
146+
int rounding = fputil::quick_get_round();
147+
if (rounding == FE_UPWARD || rounding == FE_TOWARDZERO ||
148+
(rounding == FE_TONEAREST && x_u == 0xc0f0d2f1))
149+
return -0x1.ffff'fep-1f; // -1.0f + 0x1.0p-24f
150+
151+
fputil::set_errno_if_required(ERANGE);
152+
fputil::raise_except_if_required(FE_UNDERFLOW);
153+
return -1.0f;
154+
}
155+
156+
// Exact outputs when x = 1, 2, ..., 10.
157+
// Quick check mask: 0x800f'ffffU = ~(bits of 1.0f | ... | bits of 10.0f)
158+
if (LIBC_UNLIKELY((x_u & 0x800f'ffffU) == 0)) {
159+
switch (x_u) {
160+
case 0x3f800000U: // x = 1.0f
161+
return 9.0f;
162+
case 0x40000000U: // x = 2.0f
163+
return 99.0f;
164+
case 0x40400000U: // x = 3.0f
165+
return 999.0f;
166+
case 0x40800000U: // x = 4.0f
167+
return 9'999.0f;
168+
case 0x40a00000U: // x = 5.0f
169+
return 99'999.0f;
170+
case 0x40c00000U: // x = 6.0f
171+
return 999'999.0f;
172+
case 0x40e00000U: // x = 7.0f
173+
return 9'999'999.0f;
174+
case 0x41000000U: { // x = 8.0f
175+
int rounding = fputil::quick_get_round();
176+
if (rounding == FE_UPWARD || rounding == FE_TONEAREST)
177+
return 100'000'000.0f;
178+
return 99'999'992.0f;
179+
}
180+
case 0x41100000U: { // x = 9.0f
181+
int rounding = fputil::quick_get_round();
182+
if (rounding == FE_UPWARD || rounding == FE_TONEAREST)
183+
return 1'000'000'000.0f;
184+
return 999'999'936.0f;
185+
}
186+
case 0x41200000U: { // x = 10.0f
187+
int rounding = fputil::quick_get_round();
188+
if (rounding == FE_UPWARD || rounding == FE_TONEAREST)
189+
return 10'000'000'000.0f;
190+
return 9'999'998'976.0f;
191+
}
192+
}
193+
}
194+
195+
if (auto r = EXP10M1F_EXCEPTS_HI.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
196+
return r.value();
197+
198+
// Range reduction: 10^x = 2^(mid + hi) * 10^lo
199+
// rr = (2^(mid + hi), lo)
200+
auto rr = exp_b_range_reduc<Exp10Base>(x);
201+
202+
// The low part is approximated by a degree-5 minimax polynomial.
203+
// 10^lo ~ 1 + COEFFS[0] * lo + ... + COEFFS[4] * lo^5
204+
double lo_sq = rr.lo * rr.lo;
205+
double c0 = fputil::multiply_add(rr.lo, Exp10Base::COEFFS[0], 1.0);
206+
double c1 =
207+
fputil::multiply_add(rr.lo, Exp10Base::COEFFS[2], Exp10Base::COEFFS[1]);
208+
double c2 =
209+
fputil::multiply_add(rr.lo, Exp10Base::COEFFS[4], Exp10Base::COEFFS[3]);
210+
double exp10_lo = fputil::polyeval(lo_sq, c0, c1, c2);
211+
// 10^x - 1 = 2^(mid + hi) * 10^lo - 1
212+
// ~ mh * exp10_lo - 1
213+
return static_cast<float>(fputil::multiply_add(exp10_lo, rr.mh, -1.0));
214+
}
215+
216+
} // namespace LIBC_NAMESPACE_DECL

‎libc/src/math/generic/explogxf.h

+4-4
Original file line numberDiff line numberDiff line change
@@ -159,12 +159,12 @@ template <class Base> LIBC_INLINE exp_b_reduc_t exp_b_range_reduc(float x) {
159159
int k = static_cast<int>(kd);
160160
// hi = floor(kd * 2^(-MID_BITS))
161161
// exp_hi = shift hi to the exponent field of double precision.
162-
int64_t exp_hi = static_cast<int64_t>((k >> Base::MID_BITS))
163-
<< fputil::FPBits<double>::FRACTION_LEN;
162+
uint64_t exp_hi = static_cast<uint64_t>(k >> Base::MID_BITS)
163+
<< fputil::FPBits<double>::FRACTION_LEN;
164164
// mh = 2^hi * 2^mid
165165
// mh_bits = bit field of mh
166-
int64_t mh_bits = Base::EXP_2_MID[k & Base::MID_MASK] + exp_hi;
167-
double mh = fputil::FPBits<double>(uint64_t(mh_bits)).get_val();
166+
uint64_t mh_bits = Base::EXP_2_MID[k & Base::MID_MASK] + exp_hi;
167+
double mh = fputil::FPBits<double>(mh_bits).get_val();
168168
// dx = lo = x - (hi + mid) * log(2)
169169
double dx = fputil::multiply_add(
170170
kd, Base::M_LOGB_2_LO, fputil::multiply_add(kd, Base::M_LOGB_2_HI, xd));

‎libc/test/UnitTest/FPMatcher.h

+2-1
Original file line numberDiff line numberDiff line change
@@ -174,7 +174,8 @@ template <typename T> struct FPTest : public Test {
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LIBC_NAMESPACE::cpp::numeric_limits<StorageType>::max();
175175
static constexpr T zero = FPBits::zero(Sign::POS).get_val();
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static constexpr T neg_zero = FPBits::zero(Sign::NEG).get_val();
177-
static constexpr T aNaN = FPBits::quiet_nan().get_val();
177+
static constexpr T aNaN = FPBits::quiet_nan(Sign::POS).get_val();
178+
static constexpr T neg_aNaN = FPBits::quiet_nan(Sign::NEG).get_val();
178179
static constexpr T sNaN = FPBits::signaling_nan().get_val();
179180
static constexpr T inf = FPBits::inf(Sign::POS).get_val();
180181
static constexpr T neg_inf = FPBits::inf(Sign::NEG).get_val();

‎libc/test/src/math/CMakeLists.txt

+15
Original file line numberDiff line numberDiff line change
@@ -1084,6 +1084,21 @@ add_fp_unittest(
10841084
libc.src.math.exp10m1f16
10851085
)
10861086

1087+
add_fp_unittest(
1088+
exp10m1f_test
1089+
NEED_MPFR
1090+
SUITE
1091+
libc-math-unittests
1092+
SRCS
1093+
exp10m1f_test.cpp
1094+
DEPENDS
1095+
libc.hdr.math_macros
1096+
libc.src.errno.errno
1097+
libc.src.math.exp10m1f
1098+
libc.src.__support.CPP.array
1099+
libc.src.__support.FPUtil.fp_bits
1100+
)
1101+
10871102
add_fp_unittest(
10881103
copysign_test
10891104
SUITE

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