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Diffstat (limited to 'pl/math/v_log1pf_inline.h')
-rw-r--r-- | pl/math/v_log1pf_inline.h | 55 |
1 files changed, 55 insertions, 0 deletions
diff --git a/pl/math/v_log1pf_inline.h b/pl/math/v_log1pf_inline.h new file mode 100644 index 0000000..e3048e6 --- /dev/null +++ b/pl/math/v_log1pf_inline.h @@ -0,0 +1,55 @@ +/* + * Helper for single-precision routines which calculate log(1 + x) 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_LOG1PF_INLINE_H +#define PL_MATH_V_LOG1PF_INLINE_H + +#include "v_math.h" +#include "math_config.h" + +#define Four 0x40800000 +#define Ln2 v_f32 (0x1.62e43p-1f) + +#define C(i) v_f32 (__log1pf_data.coeffs[i]) + +static inline v_f32_t +eval_poly (v_f32_t m) +{ + /* Approximate log(1+m) on [-0.25, 0.5] using Estrin scheme. */ + v_f32_t p_12 = v_fma_f32 (m, C (1), C (0)); + v_f32_t p_34 = v_fma_f32 (m, C (3), C (2)); + v_f32_t p_56 = v_fma_f32 (m, C (5), C (4)); + v_f32_t p_78 = v_fma_f32 (m, C (7), C (6)); + + v_f32_t m2 = m * m; + v_f32_t p_02 = v_fma_f32 (m2, p_12, m); + v_f32_t p_36 = v_fma_f32 (m2, p_56, p_34); + v_f32_t p_79 = v_fma_f32 (m2, C (8), p_78); + + v_f32_t m4 = m2 * m2; + v_f32_t p_06 = v_fma_f32 (m4, p_36, p_02); + + return v_fma_f32 (m4, m4 * p_79, p_06); +} + +static inline v_f32_t +log1pf_inline (v_f32_t x) +{ + /* Helper for calculating log(x + 1). Copied from log1pf_2u1.c, with no + special-case handling. See that file for details of the algorithm. */ + v_f32_t m = x + 1.0f; + v_u32_t k = (v_as_u32_f32 (m) - 0x3f400000) & 0xff800000; + v_f32_t s = v_as_f32_u32 (v_u32 (Four) - k); + v_f32_t m_scale = v_as_f32_u32 (v_as_u32_f32 (x) - k) + + v_fma_f32 (v_f32 (0.25f), s, v_f32 (-1.0f)); + v_f32_t p = eval_poly (m_scale); + v_f32_t scale_back = v_to_f32_u32 (k) * 0x1.0p-23f; + return v_fma_f32 (scale_back, Ln2, p); +} + +#endif // PL_MATH_V_LOG1PF_INLINE_H |