veclavtlica
101 lines
2.9 KiB
C
101 lines
2.9 KiB
C
/*
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Doom-inspired Q15.16 format used for most of everything.
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https://hackmd.io/9uRB9YbTSBW4Qz_2b8TyDw#Examples-2-DOOM
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*/
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#ifndef COM_FIXED_H
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#define COM_FIXED_H
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#include <stdint.h>
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#include <stdio.h>
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#define COM_FIXED_FRACBITS 16
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#define COM_FIXED_FRACUNIT (1 << COM_FIXED_FRACBITS)
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#define COM_FIXED_FRACHALF (COM_FIXED_FRACUNIT >> 1)
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#define COM_FIXED_FRACQRTR (COM_FIXED_FRACHALF >> 1)
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#define COM_FIXED_PI (com_fixed_t)205887
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#define COM_FIXED_PI2 (com_fixed_t)411774
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#define COM_FIXED_PIHALF (com_fixed_t)102943
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#define COM_FIXED_PIONEANDAHALF (COM_FIXED_PI + COM_FIXED_PIHALF)
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typedef int32_t com_fixed_t;
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extern const uint16_t com_fixed_sin_lut[128];
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static inline com_fixed_t com_fixed_add(com_fixed_t a, com_fixed_t b) {
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return a + b;
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}
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static inline com_fixed_t com_fixed_sub(com_fixed_t a, com_fixed_t b) {
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return a - b;
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}
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static inline com_fixed_t com_fixed_mul(com_fixed_t a, com_fixed_t b) {
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return (com_fixed_t)(((int64_t)a * (int64_t)b) >> COM_FIXED_FRACBITS);
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}
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/* Note: this does not clamp for over/underflow cases */
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static inline com_fixed_t com_fixed_div(com_fixed_t a, com_fixed_t b) {
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return (com_fixed_t)(((int64_t)a << COM_FIXED_FRACBITS) / (int64_t)b);
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}
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/* Is supposed to be only used for debugging, not in real code. */
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/* Because of that we default to maximum precision here. */
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static inline double com_fixed_as_float(com_fixed_t a) {
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return (a >> COM_FIXED_FRACBITS) * (double)1.0 +
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(a & 0xFFFF) * (double)(1.0 / COM_FIXED_FRACUNIT);
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}
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/* Approximated square root by Newton-Raphson in 2 iterations over small LUT. */
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com_fixed_t com_fixed_sqrt(com_fixed_t a);
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/* Approximated using LUT. */
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/* TODO: test whether linearly interpolated version could be default. */
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/* things like camera movement can be jarring if done without.*/
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/* https://namoseley.wordpress.com/2015/07/26/sincos-generation-using-table-lookup-and-iterpolation/
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*/
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static inline com_fixed_t com_fixed_sin(com_fixed_t a) {
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int32_t sign = 1;
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/* Wrap to (-Pi2,+Pi2) */
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com_fixed_t q = a % COM_FIXED_PI2;
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/* Wrap to [0,+Pi2) */
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if (q < 0)
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q = COM_FIXED_PI2 + q;
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/* Limit to [0,+1) */
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q = com_fixed_div(q, COM_FIXED_PI2);
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/* Handle cases of 3rd and 4th quadrant. */
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if (q >= COM_FIXED_FRACHALF) {
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q -= COM_FIXED_FRACHALF;
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sign = -1;
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}
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/* Finally clculate the index into LUT. */
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uint16_t const idx = q >= COM_FIXED_FRACQRTR ? 255 - (q >> 7) : q >> 7;
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return com_fixed_sin_lut[idx] * sign;
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}
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/* Implemented over sin, as to share one single LUT. */
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/* Additionally, optimizer probably can collapse some math for combined sincos
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* case. */
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static inline com_fixed_t com_fixed_cos(com_fixed_t a) {
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return com_fixed_sin(a + COM_FIXED_PIHALF);
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}
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static inline void com_fixed_sincos(com_fixed_t a, com_fixed_t *restrict s,
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com_fixed_t *restrict c) {
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*s = com_fixed_sin(a);
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*c = com_fixed_cos(a);
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}
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void com_fixed_print(com_fixed_t a);
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void com_fixed_run_tests(void);
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#endif
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