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fixed cos sin

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veclavtlica
2026-09-11 15:09:47 +03:00
parent adfae10938
commit 6d7fe7392a
10 changed files with 345 additions and 6 deletions
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Common/fixed.h
+63 -1
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@@ -7,12 +7,22 @@
#define COM_FIXED_H
#include <stdint.h>
#include <stdio.h>
#define COM_FIXED_FRACBITS 16
#define COM_FIXED_FRACUNIT (1 << COM_FIXED_FRACBITS)
#define COM_FIXED_FRACHALF (COM_FIXED_FRACUNIT >> 1)
#define COM_FIXED_FRACQRTR (COM_FIXED_FRACHALF >> 1)
#define COM_FIXED_PI (com_fixed_t)205887
#define COM_FIXED_PI2 (com_fixed_t)411774
#define COM_FIXED_PIHALF (com_fixed_t)102943
#define COM_FIXED_PIONEANDAHALF (COM_FIXED_PI + COM_FIXED_PIHALF)
typedef int32_t com_fixed_t;
extern const uint16_t com_fixed_sin_lut[128];
static inline com_fixed_t com_fixed_add(com_fixed_t a, com_fixed_t b) {
return a + b;
}
@@ -30,9 +40,61 @@ static inline com_fixed_t com_fixed_div(com_fixed_t a, com_fixed_t b) {
return (com_fixed_t)(((int64_t)a << COM_FIXED_FRACBITS) / (int64_t)b);
}
/* Approximate square root using Newton-Raphson in 2 iterations over small LUT*/
/* Is supposed to be only used for debugging, not in real code. */
/* Because of that we default to maximum precision here. */
static inline double com_fixed_as_float(com_fixed_t a) {
return (a >> COM_FIXED_FRACBITS) * (double)1.0 +
(a & 0xFFFF) * (double)(1.0 / COM_FIXED_FRACUNIT);
}
/* Approximated square root by Newton-Raphson in 2 iterations over small LUT. */
com_fixed_t com_fixed_sqrt(com_fixed_t a);
/* Approximated using LUT. */
/* TODO: test whether linearly interpolated version could be default. */
/* things like camera movement can be jarring if done without.*/
/* https://namoseley.wordpress.com/2015/07/26/sincos-generation-using-table-lookup-and-iterpolation/
*/
static inline com_fixed_t com_fixed_sin(com_fixed_t a) {
int32_t sign = 1;
/* Wrap to (-Pi2,+Pi2) */
com_fixed_t q = a % COM_FIXED_PI2;
/* Wrap to [0,+Pi2) */
if (q < 0)
q = COM_FIXED_PI2 + q;
/* Limit to [0,+1) */
q = com_fixed_div(q, COM_FIXED_PI2);
/* Handle cases of 3rd and 4th quadrant. */
if (q >= COM_FIXED_FRACHALF) {
q -= COM_FIXED_FRACHALF;
sign = -1;
}
/* Finally clculate the index into LUT. */
uint16_t const idx = q >= COM_FIXED_FRACQRTR ? 255 - (q >> 7) : q >> 7;
return com_fixed_sin_lut[idx] * sign;
}
/* Implemented over sin, as to share one single LUT. */
/* Additionally, optimizer probably can collapse some math for combined sincos
* case. */
static inline com_fixed_t com_fixed_cos(com_fixed_t a) {
return com_fixed_sin(a + COM_FIXED_PIHALF);
}
static inline void com_fixed_sincos(com_fixed_t a, com_fixed_t *restrict s,
com_fixed_t *restrict c) {
*s = com_fixed_sin(a);
*c = com_fixed_cos(a);
}
void com_fixed_print(com_fixed_t a);
void com_fixed_run_tests(void);
#endif