mirror of
https://github.com/jart/cosmopolitan.git
synced 2025-01-31 19:43:32 +00:00
46 lines
1.4 KiB
C
46 lines
1.4 KiB
C
#ifndef COSMOPOLITAN_LIBC_TINYMATH_ATANF_COMMON_H_
|
|
#define COSMOPOLITAN_LIBC_TINYMATH_ATANF_COMMON_H_
|
|
#include "libc/tinymath/atanf_data.internal.h"
|
|
#include "libc/tinymath/estrin_wrap.internal.h"
|
|
#include "libc/tinymath/hornerf.internal.h"
|
|
#if !(__ASSEMBLER__ + __LINKER__ + 0)
|
|
COSMOPOLITAN_C_START_
|
|
// clang-format off
|
|
|
|
#if WANT_VMATH
|
|
|
|
#define FLT_T float32x4_t
|
|
#define P(i) v_f32 (__atanf_poly_data.poly[i])
|
|
|
|
#else
|
|
|
|
#define FLT_T float
|
|
#define P(i) __atanf_poly_data.poly[i]
|
|
|
|
#endif
|
|
|
|
/* Polynomial used in fast atanf(x) and atan2f(y,x) implementations
|
|
The order 7 polynomial P approximates (atan(sqrt(x))-sqrt(x))/x^(3/2). */
|
|
static inline FLT_T
|
|
eval_poly (FLT_T z, FLT_T az, FLT_T shift)
|
|
{
|
|
/* Use 2-level Estrin scheme for P(z^2) with deg(P)=7. However,
|
|
a standard implementation using z8 creates spurious underflow
|
|
in the very last fma (when z^8 is small enough).
|
|
Therefore, we split the last fma into a mul and and an fma.
|
|
Horner and single-level Estrin have higher errors that exceed
|
|
threshold. */
|
|
FLT_T z2 = z * z;
|
|
FLT_T z4 = z2 * z2;
|
|
|
|
/* Then assemble polynomial. */
|
|
FLT_T y = FMA (z4, z4 * ESTRIN_3_ (z2, z4, P, 4), ESTRIN_3 (z2, z4, P));
|
|
|
|
/* Finalize:
|
|
y = shift + z * P(z^2). */
|
|
return FMA (y, z2 * az, az) + shift;
|
|
}
|
|
|
|
COSMOPOLITAN_C_END_
|
|
#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
|
|
#endif /* COSMOPOLITAN_LIBC_TINYMATH_ATANF_COMMON_H_ */
|