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[libc][math] fix-exp #148670

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[libc][math] fix-exp #148670

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14 changes: 7 additions & 7 deletions libc/src/__support/math/exp.h
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Original file line number Diff line number Diff line change
Expand Up @@ -67,7 +67,7 @@ namespace {
// Return expm1(dx) / x ~ 1 + dx / 2 + dx^2 / 6 + dx^3 / 24.
// For |dx| < 2^-13 + 2^-30:
// | output - expm1(dx) / dx | < 2^-51.
static constexpr double poly_approx_d(double dx) {
static double poly_approx_d(double dx) {
// dx^2
double dx2 = dx * dx;
// c0 = 1 + dx / 2
Expand All @@ -85,7 +85,7 @@ static constexpr double poly_approx_d(double dx) {
// Return exp(dx) ~ 1 + dx + dx^2 / 2 + ... + dx^6 / 720
// For |dx| < 2^-13 + 2^-30:
// | output - exp(dx) | < 2^-101
static constexpr DoubleDouble poly_approx_dd(const DoubleDouble &dx) {
static DoubleDouble poly_approx_dd(const DoubleDouble &dx) {
// Taylor polynomial.
constexpr DoubleDouble COEFFS[] = {
{0, 0x1p0}, // 1
Expand All @@ -106,7 +106,7 @@ static constexpr DoubleDouble poly_approx_dd(const DoubleDouble &dx) {
// Return exp(dx) ~ 1 + dx + dx^2 / 2 + ... + dx^7 / 5040
// For |dx| < 2^-13 + 2^-30:
// | output - exp(dx) | < 2^-126.
static constexpr Float128 poly_approx_f128(const Float128 &dx) {
static Float128 poly_approx_f128(const Float128 &dx) {
constexpr Float128 COEFFS_128[]{
{Sign::POS, -127, 0x80000000'00000000'00000000'00000000_u128}, // 1.0
{Sign::POS, -127, 0x80000000'00000000'00000000'00000000_u128}, // 1.0
Expand All @@ -127,7 +127,7 @@ static constexpr Float128 poly_approx_f128(const Float128 &dx) {
// Compute exp(x) using 128-bit precision.
// TODO(lntue): investigate triple-double precision implementation for this
// step.
static constexpr Float128 exp_f128(double x, double kd, int idx1, int idx2) {
static Float128 exp_f128(double x, double kd, int idx1, int idx2) {
// Recalculate dx:

double t1 = fputil::multiply_add(kd, MLOG_2_EXP2_M12_HI, x); // exact
Expand Down Expand Up @@ -160,7 +160,7 @@ static constexpr Float128 exp_f128(double x, double kd, int idx1, int idx2) {
}

// Compute exp(x) with double-double precision.
static constexpr DoubleDouble exp_double_double(double x, double kd,
static DoubleDouble exp_double_double(double x, double kd,
const DoubleDouble &exp_mid) {
// Recalculate dx:
// dx = x - k * 2^-12 * log(2)
Expand All @@ -184,7 +184,7 @@ static constexpr DoubleDouble exp_double_double(double x, double kd,

// Check for exceptional cases when
// |x| <= 2^-53 or x < log(2^-1075) or x >= 0x1.6232bdd7abcd3p+9
static constexpr double set_exceptional(double x) {
static double set_exceptional(double x) {
using FPBits = typename fputil::FPBits<double>;
FPBits xbits(x);

Expand Down Expand Up @@ -234,7 +234,7 @@ static constexpr double set_exceptional(double x) {

namespace math {

static constexpr double exp(double x) {
static double exp(double x) {
using FPBits = typename fputil::FPBits<double>;
FPBits xbits(x);

Expand Down