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Diffstat (limited to 'pl/math/v_expm1f_inline.h')
-rw-r--r-- | pl/math/v_expm1f_inline.h | 49 |
1 files changed, 49 insertions, 0 deletions
diff --git a/pl/math/v_expm1f_inline.h b/pl/math/v_expm1f_inline.h new file mode 100644 index 0000000..c261941 --- /dev/null +++ b/pl/math/v_expm1f_inline.h @@ -0,0 +1,49 @@ +/* + * Helper for single-precision routines which calculate exp(x) - 1 and do not + * need special-case handling + * + * Copyright (c) 2022-2023, Arm Limited. + * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception + */ + +#ifndef PL_MATH_V_EXPM1F_INLINE_H +#define PL_MATH_V_EXPM1F_INLINE_H + +#include "v_math.h" +#include "math_config.h" +#include "estrinf.h" + +#define One 0x3f800000 +#define Shift v_f32 (0x1.8p23f) +#define InvLn2 v_f32 (0x1.715476p+0f) +#define MLn2hi v_f32 (-0x1.62e4p-1f) +#define MLn2lo v_f32 (-0x1.7f7d1cp-20f) + +#define C(i) v_f32 (__expm1f_poly[i]) + +static inline v_f32_t +expm1f_inline (v_f32_t x) +{ + /* Helper routine for calculating exp(x) - 1. + Copied from v_expm1f_1u6.c, with all special-case handling removed - the + calling routine should handle special values if required. */ + + /* Reduce argument: f in [-ln2/2, ln2/2], i is exact. */ + v_f32_t j = v_fma_f32 (InvLn2, x, Shift) - Shift; + v_s32_t i = v_to_s32_f32 (j); + v_f32_t f = v_fma_f32 (j, MLn2hi, x); + f = v_fma_f32 (j, MLn2lo, f); + + /* Approximate expm1(f) with polynomial P, expm1(f) ~= f + f^2 * P(f). + Uses Estrin scheme, where the main __v_expm1f routine uses Horner. */ + v_f32_t f2 = f * f; + v_f32_t p = ESTRIN_4 (f, f2, f2 * f2, C); + p = v_fma_f32 (f2, p, f); + + /* t = 2^i. */ + v_f32_t t = v_as_f32_u32 (v_as_u32_s32 (i << 23) + One); + /* expm1(x) ~= p * t + (t - 1). */ + return v_fma_f32 (p, t, t - 1); +} + +#endif // PL_MATH_V_EXPM1F_INLINE_H |