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Add ULP accuracy measurement tool and documentation for vectorized math functions

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libeigen/eigen!2153

Co-authored-by: Rasmus Munk Larsen <rmlarsen@gmail.com>
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Rasmus Munk Larsen
2026-03-01 13:22:16 -08:00
parent c20b6f5c41
commit c66fc52868
5 changed files with 973 additions and 0 deletions
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78
test/ulp_accuracy/mpfr_reference.h Normal file
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// MPFR high-precision reference implementations for ULP accuracy testing.
//
// This header provides MPFR-based reference functions for all math operations
// tested by the ulp_accuracy tool. It also includes scalar conversion helpers
// between float/double and mpfr_t.
//
// Only compiled when EIGEN_HAS_MPFR is defined (i.e., MPFR and GMP are found).
#ifndef EIGEN_ULP_ACCURACY_MPFR_REFERENCE_H
#define EIGEN_ULP_ACCURACY_MPFR_REFERENCE_H
#ifdef EIGEN_HAS_MPFR
#include <mpfr.h>
// ---------------------------------------------------------------------------
// Scalar <-> mpfr_t conversion
// ---------------------------------------------------------------------------
template <typename Scalar>
static void mpfr_set_scalar(mpfr_t rop, Scalar x, mpfr_rnd_t rnd);
template <>
void mpfr_set_scalar<float>(mpfr_t rop, float x, mpfr_rnd_t rnd) {
mpfr_set_flt(rop, x, rnd);
}
template <>
void mpfr_set_scalar<double>(mpfr_t rop, double x, mpfr_rnd_t rnd) {
mpfr_set_d(rop, x, rnd);
}
template <typename Scalar>
static Scalar mpfr_get_scalar(mpfr_t op, mpfr_rnd_t rnd);
template <>
float mpfr_get_scalar<float>(mpfr_t op, mpfr_rnd_t rnd) {
return mpfr_get_flt(op, rnd);
}
template <>
double mpfr_get_scalar<double>(mpfr_t op, mpfr_rnd_t rnd) {
return mpfr_get_d(op, rnd);
}
// ---------------------------------------------------------------------------
// MPFR wrappers for functions not directly provided by libmpfr
// ---------------------------------------------------------------------------
// logistic(x) = 1 / (1 + exp(-x))
static int mpfr_logistic(mpfr_t rop, const mpfr_t op, mpfr_rnd_t rnd) {
mpfr_t tmp, one;
mpfr_init2(tmp, mpfr_get_prec(rop));
mpfr_init2(one, mpfr_get_prec(rop));
mpfr_set_ui(one, 1, rnd);
mpfr_neg(tmp, op, rnd);
mpfr_exp(tmp, tmp, rnd);
mpfr_add(tmp, tmp, one, rnd);
int ret = mpfr_div(rop, one, tmp, rnd);
mpfr_clear(tmp);
mpfr_clear(one);
return ret;
}
// rsqrt(x) = 1 / sqrt(x)
static int mpfr_rsqrt(mpfr_t rop, const mpfr_t op, mpfr_rnd_t rnd) { return mpfr_rec_sqrt(rop, op, rnd); }
// exp2(x) = 2^x
static int mpfr_exp2_wrap(mpfr_t rop, const mpfr_t op, mpfr_rnd_t rnd) {
mpfr_t two;
mpfr_init2(two, mpfr_get_prec(rop));
mpfr_set_ui(two, 2, rnd);
int ret = mpfr_pow(rop, two, op, rnd);
mpfr_clear(two);
return ret;
}
// log2(x) — thin wrapper to match the function signature convention.
static int mpfr_log2_wrap(mpfr_t rop, const mpfr_t op, mpfr_rnd_t rnd) { return mpfr_log2(rop, op, rnd); }
#endif // EIGEN_HAS_MPFR
#endif // EIGEN_ULP_ACCURACY_MPFR_REFERENCE_H