[libc-commits] [libc] [libc][math][c23] Add exp10m1f C23 math function (PR #87992)
via libc-commits
libc-commits at lists.llvm.org
Tue Apr 9 05:43:10 PDT 2024
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@@ -0,0 +1,215 @@
+//===-- Implementation of exp10m1f function -------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/math/exp10m1f.h"
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/PolyEval.h"
+#include "src/__support/FPUtil/except_value_utils.h"
+#include "src/__support/FPUtil/multiply_add.h"
+#include "src/__support/FPUtil/rounding_mode.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/optimization.h"
+#include "src/errno/libc_errno.h"
+
+#include "explogxf.h"
+
+namespace LIBC_NAMESPACE {
+
+static constexpr size_t N_EXCEPTS_LO = 11;
+
+static constexpr fputil::ExceptValues<float, N_EXCEPTS_LO> EXP10M1F_EXCEPTS_LO =
+ {{
+ // x = 0x1.0fe54ep-11, exp10m1f(x) = 0x1.3937eep-10 (RZ)
+ {0x3a07'f2a7U, 0x3a9c'9bf7U, 1U, 0U, 1U},
+ // x = 0x1.80e6eap-11, exp10m1f(x) = 0x1.bb8272p-10 (RZ)
+ {0x3a40'7375U, 0x3add'c139U, 1U, 0U, 1U},
+ // x = -0x1.2a33bcp-51, exp10m1f(x) = -0x1.57515ep-50 (RZ)
+ {0xa615'19deU, 0xa6ab'a8afU, 0U, 1U, 0U},
+ // x = -0x0p+0, exp10m1f(x) = -0x0p+0 (RZ)
+ {0x8000'0000U, 0x8000'0000U, 0U, 0U, 0U},
+ // x = -0x1.b59e08p-31, exp10m1f(x) = -0x1.f7d356p-30 (RZ)
+ {0xb05a'cf04U, 0xb0fb'e9abU, 0U, 1U, 1U},
+ // x = -0x1.bf342p-12, exp10m1f(x) = -0x1.014e02p-10 (RZ)
+ {0xb9df'9a10U, 0xba80'a701U, 0U, 1U, 0U},
+ // x = -0x1.6207fp-11, exp10m1f(x) = -0x1.9746cap-10 (RZ)
+ {0xba31'03f8U, 0xbacb'a365U, 0U, 1U, 1U},
+ // x = -0x1.bd0c66p-11, exp10m1f(x) = -0x1.ffe168p-10 (RZ)
+ {0xba5e'8633U, 0xbaff'f0b4U, 0U, 1U, 1U},
+ // x = -0x1.ffd84cp-10, exp10m1f(x) = -0x1.25faf2p-8 (RZ)
+ {0xbaff'ec26U, 0xbb92'fd79U, 0U, 1U, 0U},
+ // x = -0x1.a74172p-9, exp10m1f(x) = -0x1.e57be2p-8 (RZ)
+ {0xbb53'a0b9U, 0xbbf2'bdf1U, 0U, 1U, 1U},
+ // x = -0x1.cb694cp-9, exp10m1f(x) = -0x1.0764e4p-7 (RZ)
+ {0xbb65'b4a6U, 0xbc03'b272U, 0U, 1U, 0U},
+ }};
+
+static constexpr size_t N_EXCEPTS_HI = 19;
+
+static constexpr fputil::ExceptValues<float, N_EXCEPTS_HI> EXP10M1F_EXCEPTS_HI =
+ {{
+ // (input, RZ output, RU offset, RD offset, RN offset)
+ // x = 0x1.8d31eep-8, exp10m1f(x) = 0x1.cc7e4cp-7 (RZ)
+ {0x3bc6'98f7U, 0x3c66'3f26U, 1U, 0U, 1U},
+ // x = 0x1.915fcep-8, exp10m1f(x) = 0x1.d15f72p-7 (RZ)
+ {0x3bc8'afe7U, 0x3c68'afb9U, 1U, 0U, 0U},
+ // x = 0x1.bcf982p-8, exp10m1f(x) = 0x1.022928p-6 (RZ)
+ {0x3bde'7cc1U, 0x3c81'1494U, 1U, 0U, 1U},
+ // x = 0x1.99ff0ap-7, exp10m1f(x) = 0x1.dee416p-6 (RZ)
+ {0x3c4c'ff85U, 0x3cef'720bU, 1U, 0U, 0U},
+ // x = 0x1.75ea14p-6, exp10m1f(x) = 0x1.b9ff16p-5 (RZ)
+ {0x3cba'f50aU, 0x3d5c'ff8bU, 1U, 0U, 0U},
+ // x = 0x1.f81b64p-6, exp10m1f(x) = 0x1.2cb6bcp-4 (RZ)
+ {0x3cfc'0db2U, 0x3d96'5b5eU, 1U, 0U, 0U},
+ // x = 0x1.fafecp+3, exp10m1f(x) = 0x1.8c880ap+52 (RZ)
+ {0x417d'7f60U, 0x59c6'4405U, 1U, 0U, 0U},
+ // x = -0x1.3bf094p-8, exp10m1f(x) = -0x1.69ba4ap-7 (RZ)
+ {0xbb9d'f84aU, 0xbc34'dd25U, 0U, 1U, 0U},
+ // x = -0x1.4558bcp-8, exp10m1f(x) = -0x1.746fb8p-7 (RZ)
+ {0xbba2'ac5eU, 0xbc3a'37dcU, 0U, 1U, 1U},
+ // x = -0x1.4bb43p-8, exp10m1f(x) = -0x1.7babe4p-7 (RZ)
+ {0xbba5'da18U, 0xbc3d'd5f2U, 0U, 1U, 1U},
+ // x = -0x1.776cc8p-8, exp10m1f(x) = -0x1.ad62c4p-7 (RZ)
+ {0xbbbb'b664U, 0xbc56'b162U, 0U, 1U, 0U},
+ // x = -0x1.f024cp-8, exp10m1f(x) = -0x1.1b20d6p-6 (RZ)
+ {0xbbf8'1260U, 0xbc8d'906bU, 0U, 1U, 1U},
+ // x = -0x1.f510eep-8, exp10m1f(x) = -0x1.1de9aap-6 (RZ)
+ {0xbbfa'8877U, 0xbc8e'f4d5U, 0U, 1U, 0U},
+ // x = -0x1.0b43c4p-7, exp10m1f(x) = -0x1.30d418p-6 (RZ)
+ {0xbc05'a1e2U, 0xbc98'6a0cU, 0U, 1U, 0U},
+ // x = -0x1.245ee4p-7, exp10m1f(x) = -0x1.4d2b86p-6 (RZ)
+ {0xbc12'2f72U, 0xbca6'95c3U, 0U, 1U, 0U},
+ // x = -0x1.f9f2dap-7, exp10m1f(x) = -0x1.1e2186p-5 (RZ)
+ {0xbc7c'f96dU, 0xbd0f'10c3U, 0U, 1U, 0U},
+ // x = -0x1.08e42p-6, exp10m1f(x) = -0x1.2b5c4p-5 (RZ)
+ {0xbc84'7210U, 0xbd15'ae20U, 0U, 1U, 1U},
+ // x = -0x1.0cdc44p-5, exp10m1f(x) = -0x1.2a2152p-4 (RZ)
+ {0xbd06'6e22U, 0xbd95'10a9U, 0U, 1U, 1U},
+ // x = -0x1.ca4322p-5, exp10m1f(x) = -0x1.ef073p-4 (RZ)
+ {0xbd65'2191U, 0xbdf7'8398U, 0U, 1U, 1U},
+ }};
+
+LLVM_LIBC_FUNCTION(float, exp10m1f, (float x)) {
+ using FPBits = fputil::FPBits<float>;
+ FPBits xbits(x);
+
+ uint32_t x_u = xbits.uintval();
+ uint32_t x_abs = x_u & 0x7fff'ffffU;
+
+ // When x >= log10(2^128), or x is nan
+ if (LIBC_UNLIKELY(xbits.is_pos() && x_u >= 0x421a'209bU)) {
+ if (xbits.is_finite()) {
+ int rounding = fputil::quick_get_round();
+ if (rounding == FE_DOWNWARD || rounding == FE_TOWARDZERO)
+ return FPBits::max_normal().get_val();
+
+ fputil::set_errno_if_required(ERANGE);
+ fputil::raise_except_if_required(FE_OVERFLOW);
+ }
+
+ // x >= log10(2^128) and 10^x - 1 rounds to +inf, or x is +inf or nan
+ return x + FPBits::inf().get_val();
+ }
+
+ // When |x| <= log10(2) * 2^(-6)
+ if (LIBC_UNLIKELY(x_abs <= 0x3b9a'209bU)) {
+ if (auto r = EXP10M1F_EXCEPTS_LO.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
+ return r.value();
+
+ double dx = x;
+ double dx_sq = dx * dx;
+ double c0 = dx * Exp10Base::COEFFS[0];
+ double c1 =
+ fputil::multiply_add(dx, Exp10Base::COEFFS[2], Exp10Base::COEFFS[1]);
+ double c2 =
+ fputil::multiply_add(dx, Exp10Base::COEFFS[4], Exp10Base::COEFFS[3]);
+ // 10^dx - 1 ~ (1 + COEFFS[0] * dx + ... + COEFFS[4] * dx^5) - 1
+ // = COEFFS[0] * dx + ... + COEFFS[4] * dx^5
+ return static_cast<float>(fputil::polyeval(dx_sq, c0, c1, c2));
+ }
+
+ // When x <= log10(2^-25), or x is nan
+ if (LIBC_UNLIKELY(x <= -0x1.e1a5e2p+2f)) {
+ // exp10m1(-inf) = -1
+ if (xbits.is_inf())
+ return -1.0f;
+ // exp10m1(nan) = nan
+ if (xbits.is_nan())
----------------
lntue wrote:
When the function is called with a NaN, it will hit L116, and we return `x + Inf`, which would return the same NaN as `x`.
https://github.com/llvm/llvm-project/pull/87992
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