fixed32.h

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#ifndef OPENSNES_FIXED32_H
#define OPENSNES_FIXED32_H
 
#include <snes/types.h>
#include <snes/math.h>   /* for fixSin / fixCos (8.8 LUT) */
 
/*============================================================================
 * Type and macros
 *============================================================================*/

typedef s32 fixed32;

/* Cast through u32 before shifting to avoid the C UB on left-shifting a
 * negative signed value. Final cast back to fixed32 preserves bit pattern. */
#define FIX32(x) ((fixed32)((u32)(s32)(x) << 16))

#define UNFIX32(x) ((s16)((fixed32)(x) >> 16))

#define FIX32_FRAC(x) ((u16)((fixed32)(x) & 0xFFFF))

#define FIX32_MAKE(i, f) (((fixed32)(s16)(i) << 16) | (fixed32)(u16)(f))
 
/*============================================================================
 * Inline operations (no asm needed — compiler emits Kl arithmetic)
 *============================================================================*/

inline fixed32 fix32Abs(fixed32 x) {
    return x < 0 ? -x : x;
}

inline fixed32 fix32Clamp(fixed32 x, fixed32 min, fixed32 max) {
    if (x < min) return min;
    if (x > max) return max;
    return x;
}

inline fixed32 fix32Min(fixed32 a, fixed32 b) {
    return a < b ? a : b;
}

inline fixed32 fix32Max(fixed32 a, fixed32 b) {
    return a > b ? a : b;
}
 
/*============================================================================
 * ASM-backed multiply
 *============================================================================*/

fixed32 fix32Mul(fixed32 a, fixed32 b);

fixed32 fix32Div(fixed32 a, fixed32 b);

inline fixed32 fix32Lerp(fixed32 a, fixed32 b, fixed32 t) {
    return a + fix32Mul(b - a, t);
}
 
/*============================================================================
 * Trigonometry (lifted from 8.8 LUT, 8 fractional bits of precision)
 *============================================================================*/

/* Implemented in lib/source/fixed32.asm. Two qbe codegen bugs make the
 * one-line C body `(u32)(s32)fixSin(angle) << 8` produce wrong results:
 *
 *   1. Kl shift-by-constant spill (fixed in qbe 2026-05-22): the high
 *      half was computed from an unstored stack slot. Resolved.
 *
 *   2. Kw → Kl widening sign assumption (UNFIXED): ref_is_high_zero()
 *      treats all Kw operands as zero-extended. Wrong for signed
 *      s16 → s32 — produces 0x00FF0000 instead of 0xFFFF0000 for
 *      sin(270°) = -1.
 *
 * The asm form sign-extends explicitly and avoids both. See
 * lib/source/math.c for the full notes. */
fixed32 fix32Sin(u8 angle);
fixed32 fix32Cos(u8 angle);

/* fix32Cos declared above with fix32Sin — both bodies in math.c. */
 
#endif /* OPENSNES_FIXED32_H */