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Optimize erf function with expm1f in Metal backend #3025

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Merged
awni merged 1 commit into from
Jan 20, 2026
Merged

Optimize erf function with expm1f in Metal backend #3025

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4 changes: 2 additions & 2 deletions mlx/backend/metal/kernels/erf.h
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@

#pragma once
#include <metal_math>
#include "mlx/backend/metal/kernels/expm1f.h"

/*
* Approximation to the error function.
Expand All @@ -23,8 +24,7 @@ float erf(float a) {
r = metal::fma(r, t, -6.34846687e-1f); // -0x1.450aa0p-1
r = metal::fma(r, t, -1.28717512e-1f); // -0x1.079d0cp-3
r = metal::fma(r, t, -t);
// TODO, replace with expm1 when implemented
r = 1.0f - metal::exp(r);
r = -expm1f(r);
r = metal::copysign(r, a);
} else {
// maximum error 0.98929 ulp
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