1 /*
2  * Double-precision polynomial evaluation function for scalar and vector atan(x)
3  * and atan2(y,x).
4  *
5  * Copyright (c) 2021-2023, Arm Limited.
6  * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception
7  */
8 
9 #include "math_config.h"
10 #include "estrin.h"
11 
12 #if V_SUPPORTED
13 
14 #include "v_math.h"
15 
16 #define DBL_T v_f64_t
17 #define P(i) v_f64 (__atan_poly_data.poly[i])
18 
19 #else
20 
21 #define DBL_T double
22 #define P(i) __atan_poly_data.poly[i]
23 
24 #endif
25 
26 /* Polynomial used in fast atan(x) and atan2(y,x) implementations
27    The order 19 polynomial P approximates (atan(sqrt(x))-sqrt(x))/x^(3/2).  */
28 static inline DBL_T
29 eval_poly (DBL_T z, DBL_T az, DBL_T shift)
30 {
31   /* Use split Estrin scheme for P(z^2) with deg(P)=19. Use split instead of
32      full scheme to avoid underflow in x^16.  */
33   DBL_T z2 = z * z;
34   DBL_T x2 = z2 * z2;
35   DBL_T x4 = x2 * x2;
36   DBL_T x8 = x4 * x4;
37   DBL_T y
38     = FMA (ESTRIN_11_ (z2, x2, x4, x8, P, 8), x8, ESTRIN_7 (z2, x2, x4, P));
39 
40   /* Finalize. y = shift + z + z^3 * P(z^2).  */
41   y = FMA (y, z2 * az, az);
42   y = y + shift;
43 
44   return y;
45 }
46 
47 #undef DBL_T
48 #undef FMA
49 #undef P
50