1 /* 2 * Helper for single-precision routines which calculate log(1 + x) and do not 3 * need special-case handling 4 * 5 * Copyright (c) 2022-2023, Arm Limited. 6 * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception 7 */ 8 9 #ifndef PL_MATH_V_LOG1PF_INLINE_H 10 #define PL_MATH_V_LOG1PF_INLINE_H 11 12 #include "v_math.h" 13 #include "math_config.h" 14 15 #define Four 0x40800000 16 #define Ln2 v_f32 (0x1.62e43p-1f) 17 18 #define C(i) v_f32 (__log1pf_data.coeffs[i]) 19 20 static inline v_f32_t 21 eval_poly (v_f32_t m) 22 { 23 /* Approximate log(1+m) on [-0.25, 0.5] using Estrin scheme. */ 24 v_f32_t p_12 = v_fma_f32 (m, C (1), C (0)); 25 v_f32_t p_34 = v_fma_f32 (m, C (3), C (2)); 26 v_f32_t p_56 = v_fma_f32 (m, C (5), C (4)); 27 v_f32_t p_78 = v_fma_f32 (m, C (7), C (6)); 28 29 v_f32_t m2 = m * m; 30 v_f32_t p_02 = v_fma_f32 (m2, p_12, m); 31 v_f32_t p_36 = v_fma_f32 (m2, p_56, p_34); 32 v_f32_t p_79 = v_fma_f32 (m2, C (8), p_78); 33 34 v_f32_t m4 = m2 * m2; 35 v_f32_t p_06 = v_fma_f32 (m4, p_36, p_02); 36 37 return v_fma_f32 (m4, m4 * p_79, p_06); 38 } 39 40 static inline v_f32_t 41 log1pf_inline (v_f32_t x) 42 { 43 /* Helper for calculating log(x + 1). Copied from log1pf_2u1.c, with no 44 special-case handling. See that file for details of the algorithm. */ 45 v_f32_t m = x + 1.0f; 46 v_u32_t k = (v_as_u32_f32 (m) - 0x3f400000) & 0xff800000; 47 v_f32_t s = v_as_f32_u32 (v_u32 (Four) - k); 48 v_f32_t m_scale = v_as_f32_u32 (v_as_u32_f32 (x) - k) 49 + v_fma_f32 (v_f32 (0.25f), s, v_f32 (-1.0f)); 50 v_f32_t p = eval_poly (m_scale); 51 v_f32_t scale_back = v_to_f32_u32 (k) * 0x1.0p-23f; 52 return v_fma_f32 (scale_back, Ln2, p); 53 } 54 55 #endif // PL_MATH_V_LOG1PF_INLINE_H 56