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[libc][math] Refactor exp2 implementation to header-only in src/__support/math folder. #161297

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[libc][math] Refactor exp2 implementation to header-only in src/__support/math folder. #161297

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1 change: 1 addition & 0 deletions libc/shared/math.h
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Original file line number Diff line number Diff line change
Expand Up @@ -47,6 +47,7 @@
#include "math/exp10f16.h"
#include "math/exp10m1f.h"
#include "math/exp10m1f16.h"
#include "math/exp2.h"
#include "math/expf.h"
#include "math/expf16.h"
#include "math/frexpf.h"
Expand Down
23 changes: 23 additions & 0 deletions libc/shared/math/exp2.h
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Original file line number Diff line number Diff line change
@@ -0,0 +1,23 @@
//===-- Shared exp2 function ------------------------------------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_LIBC_SHARED_MATH_EXP2_H
#define LLVM_LIBC_SHARED_MATH_EXP2_H

#include "shared/libc_common.h"
#include "src/__support/math/exp2.h"

namespace LIBC_NAMESPACE_DECL {
namespace shared {

using math::exp2;

} // namespace shared
} // namespace LIBC_NAMESPACE_DECL

#endif // LLVM_LIBC_SHARED_MATH_EXP2_H
31 changes: 31 additions & 0 deletions libc/src/__support/math/CMakeLists.txt
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Expand Up @@ -373,6 +373,15 @@ add_header_library(
libc.src.__support.macros.optimization
)

add_header_library(
common_constants
HDRS
common_constants.h
DEPENDS
libc.src.__support.macros.config
libc.src.__support.number_pair
)

add_header_library(
cos
HDRS
Expand Down Expand Up @@ -704,6 +713,28 @@ add_header_library(
libc.src.__support.macros.optimization
)

add_header_library(
exp2
HDRS
exp2.h
DEPENDS
.common_constants
.exp_utils
libc.src.__support.CPP.bit
libc.src.__support.CPP.optional
libc.src.__support.FPUtil.dyadic_float
libc.src.__support.FPUtil.fenv_impl
libc.src.__support.FPUtil.fp_bits
libc.src.__support.FPUtil.multiply_add
libc.src.__support.FPUtil.nearest_integer
libc.src.__support.FPUtil.polyeval
libc.src.__support.FPUtil.rounding_mode
libc.src.__support.FPUtil.triple_double
libc.src.__support.integer_literals
libc.src.__support.macros.optimization
libc.src.errno.errno
)

add_header_library(
exp10
HDRS
Expand Down
47 changes: 34 additions & 13 deletions libc/src/math/generic/common_constants.cpp → libc/src/__support/math/common_constants.h
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Expand Up @@ -6,20 +6,37 @@
//
//===----------------------------------------------------------------------===//

#include "common_constants.h"
#ifndef LLVM_LIBC_SRC___SUPPORT_MATH_COMMON_CONSTANTS_H
#define LLVM_LIBC_SRC___SUPPORT_MATH_COMMON_CONSTANTS_H

#include "src/__support/macros/config.h"
#include "src/__support/number_pair.h"

namespace LIBC_NAMESPACE_DECL {

namespace common_constants_internal {

// log(2) generated by Sollya with:
// > a = 2^-43 * nearestint(2^43*log(2));
// LSB = 2^-43 is chosen so that e_x * LOG_2_HI is exact for -1075 < e_x < 1024.
static constexpr double LOG_2_HI = 0x1.62e42fefa38p-1; // LSB = 2^-43
// > b = round(log10(2) - a, D, RN);
static constexpr double LOG_2_LO = 0x1.ef35793c7673p-45; // LSB = 2^-97

// Minimax polynomial for (log(1 + x) - x)/x^2, generated by sollya with:
// > P = fpminimax((log(1 + x) - x)/x^2, 5, [|D...|], [-2^-8, 2^-7]);
constexpr double LOG_COEFFS[6] = {-0x1.fffffffffffffp-2, 0x1.5555555554a9bp-2,
-0x1.0000000094567p-2, 0x1.99999dcc9823cp-3,
-0x1.55550ac2e537ap-3, 0x1.21a02c4e624d7p-3};

// Range reduction constants for logarithms.
// r(0) = 1, r(127) = 0.5
// r(k) = 2^-8 * ceil(2^8 * (1 - 2^-8) / (1 + k*2^-7))
// The constants are chosen so that v = fma(r, m_x, -1) is exact in single
// precision, and -2^-8 <= v < 2^-7.
// TODO(lntue): Add reference to how the constants are derived after the
// resulting paper is ready.
alignas(8) const float R[128] = {
alignas(8) static constexpr float R[128] = {
0x1p0, 0x1.fcp-1, 0x1.f8p-1, 0x1.f4p-1, 0x1.fp-1, 0x1.ecp-1, 0x1.e8p-1,
0x1.e4p-1, 0x1.ep-1, 0x1.dep-1, 0x1.dap-1, 0x1.d6p-1, 0x1.d4p-1, 0x1.dp-1,
0x1.ccp-1, 0x1.cap-1, 0x1.c6p-1, 0x1.c4p-1, 0x1.cp-1, 0x1.bep-1, 0x1.bap-1,
Expand All @@ -40,7 +57,7 @@ alignas(8) const float R[128] = {
0x1.0ap-1, 0x1.08p-1, 0x1.08p-1, 0x1.06p-1, 0x1.06p-1, 0x1.04p-1, 0x1.04p-1,
0x1.02p-1, 0x1.0p-1};

const double RD[128] = {
static constexpr double RD[128] = {
0x1p0, 0x1.fcp-1, 0x1.f8p-1, 0x1.f4p-1, 0x1.fp-1, 0x1.ecp-1, 0x1.e8p-1,
0x1.e4p-1, 0x1.ep-1, 0x1.dep-1, 0x1.dap-1, 0x1.d6p-1, 0x1.d4p-1, 0x1.dp-1,
0x1.ccp-1, 0x1.cap-1, 0x1.c6p-1, 0x1.c4p-1, 0x1.cp-1, 0x1.bep-1, 0x1.bap-1,
Expand All @@ -65,7 +82,7 @@ const double RD[128] = {
// available.
// Generated by Sollya with the formula: CD[i] = RD[i]*(1 + i*2^-7) - 1
// for RD[i] defined on the table above.
const double CD[128] = {
static constexpr double CD[128] = {
0.0, -0x1p-14, -0x1p-12, -0x1.2p-11, -0x1p-10, -0x1.9p-10,
-0x1.2p-9, -0x1.88p-9, -0x1p-8, -0x1.9p-11, -0x1.fp-10, -0x1.9cp-9,
-0x1p-12, -0x1.cp-10, -0x1.bp-9, -0x1.5p-11, -0x1.4p-9, 0x1p-14,
Expand All @@ -90,7 +107,7 @@ const double CD[128] = {
-0x1p-14, -0x1p-8,
};

const double LOG_R[128] = {
static constexpr double LOG_R[128] = {
0x0.0000000000000p0, 0x1.010157588de71p-7, 0x1.0205658935847p-6,
0x1.8492528c8cabfp-6, 0x1.0415d89e74444p-5, 0x1.466aed42de3eap-5,
0x1.894aa149fb343p-5, 0x1.ccb73cdddb2ccp-5, 0x1.08598b59e3a07p-4,
Expand Down Expand Up @@ -135,7 +152,7 @@ const double LOG_R[128] = {
0x1.5707a26bb8c66p-1, 0x1.5af405c3649ep-1, 0x1.5af405c3649ep-1,
0x1.5ee82aa24192p-1, 0x0.000000000000p0};

const double LOG2_R[128] = {
static constexpr double LOG2_R[128] = {
0x0.0000000000000p+0, 0x1.72c7ba20f7327p-7, 0x1.743ee861f3556p-6,
0x1.184b8e4c56af8p-5, 0x1.77394c9d958d5p-5, 0x1.d6ebd1f1febfep-5,
0x1.1bb32a600549dp-4, 0x1.4c560fe68af88p-4, 0x1.7d60496cfbb4cp-4,
Expand Down Expand Up @@ -188,7 +205,7 @@ const double LOG2_R[128] = {
// print("{", -c, ",", -b, "},");
// };
// We replace LOG_R[0] with log10(1.0) == 0.0
alignas(16) const NumberPair<double> LOG_R_DD[128] = {
alignas(16) static constexpr NumberPair<double> LOG_R_DD[128] = {
{0.0, 0.0},
{-0x1.0c76b999d2be8p-46, 0x1.010157589p-7},
{-0x1.3dc5b06e2f7d2p-45, 0x1.0205658938p-6},
Expand Down Expand Up @@ -324,7 +341,7 @@ alignas(16) const NumberPair<double> LOG_R_DD[128] = {
// Output range:
// [-0x1.3ffcp-15, 0x1.3e3dp-15]
// We store S2[i] = 2^16 (r(i - 2^6) - 1).
alignas(8) const int S2[193] = {
alignas(8) static constexpr int S2[193] = {
0x101, 0xfd, 0xf9, 0xf5, 0xf1, 0xed, 0xe9, 0xe5, 0xe1,
0xdd, 0xd9, 0xd5, 0xd1, 0xcd, 0xc9, 0xc5, 0xc1, 0xbd,
0xb9, 0xb4, 0xb0, 0xac, 0xa8, 0xa4, 0xa0, 0x9c, 0x98,
Expand All @@ -348,7 +365,7 @@ alignas(8) const int S2[193] = {
-0x1cd, -0x1d1, -0x1d5, -0x1d9, -0x1dd, -0x1e0, -0x1e4, -0x1e8, -0x1ec,
-0x1f0, -0x1f4, -0x1f8, -0x1fc};

const double R2[193] = {
static constexpr double R2[193] = {
0x1.0101p0, 0x1.00fdp0, 0x1.00f9p0, 0x1.00f5p0, 0x1.00f1p0,
0x1.00edp0, 0x1.00e9p0, 0x1.00e5p0, 0x1.00e1p0, 0x1.00ddp0,
0x1.00d9p0, 0x1.00d5p0, 0x1.00d1p0, 0x1.00cdp0, 0x1.00c9p0,
Expand Down Expand Up @@ -395,7 +412,7 @@ const double R2[193] = {
// Output range:
// [-0x1.01928p-22 , 0x1p-22]
// We store S[i] = 2^21 (r(i - 80) - 1).
alignas(8) const int S3[161] = {
alignas(8) static constexpr int S3[161] = {
0x50, 0x4f, 0x4e, 0x4d, 0x4c, 0x4b, 0x4a, 0x49, 0x48, 0x47, 0x46,
0x45, 0x44, 0x43, 0x42, 0x41, 0x40, 0x3f, 0x3e, 0x3d, 0x3c, 0x3b,
0x3a, 0x39, 0x38, 0x37, 0x36, 0x35, 0x34, 0x33, 0x32, 0x31, 0x30,
Expand All @@ -418,7 +435,7 @@ alignas(8) const int S3[161] = {
// Output range:
// [-0x1.0002143p-29 , 0x1p-29]
// We store S[i] = 2^28 (r(i - 65) - 1).
alignas(8) const int S4[130] = {
alignas(8) static constexpr int S4[130] = {
0x41, 0x40, 0x3f, 0x3e, 0x3d, 0x3c, 0x3b, 0x3a, 0x39, 0x38, 0x37,
0x36, 0x35, 0x34, 0x33, 0x32, 0x31, 0x30, 0x2f, 0x2e, 0x2d, 0x2c,
0x2b, 0x2a, 0x29, 0x28, 0x27, 0x26, 0x25, 0x24, 0x23, 0x22, 0x21,
Expand All @@ -439,7 +456,7 @@ alignas(8) const int S4[130] = {
// Table is generated with Sollya as follow:
// > display = hexadecimal;
// > for i from -104 to 89 do { D(exp(i)); };
const double EXP_M1[195] = {
static constexpr double EXP_M1[195] = {
0x1.f1e6b68529e33p-151, 0x1.525be4e4e601dp-149, 0x1.cbe0a45f75eb1p-148,
0x1.3884e838aea68p-146, 0x1.a8c1f14e2af5dp-145, 0x1.20a717e64a9bdp-143,
0x1.8851d84118908p-142, 0x1.0a9bdfb02d240p-140, 0x1.6a5bea046b42ep-139,
Expand Down Expand Up @@ -511,7 +528,7 @@ const double EXP_M1[195] = {
// Table is generated with Sollya as follow:
// > display = hexadecimal;
// > for i from 0 to 127 do { D(exp(i / 128)); };
const double EXP_M2[128] = {
static constexpr double EXP_M2[128] = {
0x1.0000000000000p0, 0x1.0202015600446p0, 0x1.04080ab55de39p0,
0x1.06122436410ddp0, 0x1.08205601127edp0, 0x1.0a32a84e9c1f6p0,
0x1.0c49236829e8cp0, 0x1.0e63cfa7ab09dp0, 0x1.1082b577d34edp0,
Expand Down Expand Up @@ -557,4 +574,8 @@ const double EXP_M2[128] = {
0x1.568bb722dd593p1, 0x1.593b7d72305bbp1,
};

} // namespace common_constants_internal

} // namespace LIBC_NAMESPACE_DECL

#endif // LLVM_LIBC_SRC___SUPPORT_MATH_COMMON_CONSTANTS_H
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