rockbox/apps/fracmul.h

#ifndef _FRACMUL_H
#define _FRACMUL_H

#include <stdint.h>
#include "gcc_extensions.h"

/** FRACTIONAL MULTIPLICATION
 *  Multiply two fixed point numbers with 31 fractional bits:
 *      FRACMUL(x, y)
 *
 *  Multiply two fixed point numbers with 31 fractional bits,
 *          then shift left by z bits:
 *      FRACMUL_SHL(x, y, z)
 *          NOTE: z must be in the range 1-8 on Coldfire targets.
 */


/* A bunch of fixed point assembler helper macros */
#if defined(CPU_COLDFIRE)
/* These macros use the Coldfire EMAC extension and need the MACSR flags set
 * to fractional mode with no rounding.
 */

/* Multiply two S.31 fractional integers and return the sign bit and the
 * 31 most significant bits of the result.
 */
static inline int32_t FRACMUL(int32_t x, int32_t y)
{
    int32_t t;
    asm ("mac.l    %[a], %[b], %%acc0\n\t"
         "movclr.l %%acc0, %[t]\n\t"
         : [t] "=r" (t) : [a] "r" (x), [b] "r" (y));
    return t;
}

/* Multiply two S.31 fractional integers, and return the 32 most significant
 * bits after a shift left by the constant z. NOTE: Only works for shifts of
 * 1 to 8 on Coldfire!
 */
static FORCE_INLINE int32_t FRACMUL_SHL(int32_t x, int32_t y, int z)
{
    int32_t t, t2;
    asm ("mac.l    %[a], %[b], %%acc0\n\t"
         "move.l   %[d], %[t]\n\t"
         "move.l   %%accext01, %[t2]\n\t"
         "and.l    %[mask], %[t2]\n\t"
         "lsr.l    %[t], %[t2]\n\t"
         "movclr.l %%acc0, %[t]\n\t"
         "asl.l    %[c], %[t]\n\t"
         "or.l     %[t2], %[t]\n\t"
         : [t] "=&d" (t), [t2] "=&d" (t2)
         : [a] "r" (x), [b] "r" (y), [mask] "d" (0xff),
           [c] "id" ((z)), [d] "id" (8 - (z)));
    return t;
}

#elif defined(CPU_ARM)

/* Multiply two S.31 fractional integers and return the sign bit and the
 * 31 most significant bits of the result.
 */
static inline int32_t FRACMUL(int32_t x, int32_t y)
{
    int32_t t, t2;
    asm ("smull    %[t], %[t2], %[a], %[b]\n\t"
         "mov      %[t2], %[t2], asl #1\n\t"
         "orr      %[t], %[t2], %[t], lsr #31\n\t"
         : [t] "=&r" (t), [t2] "=&r" (t2)
         : [a] "r" (x), [b] "r" (y));
    return t;
}

/* Multiply two S.31 fractional integers, and return the 32 most significant
 * bits after a shift left by the constant z.
 */
static FORCE_INLINE int32_t FRACMUL_SHL(int32_t x, int32_t y, int z)
{
    int32_t t, t2;
    asm ("smull    %[t], %[t2], %[a], %[b]\n\t"
         "mov      %[t2], %[t2], asl %[c]\n\t"
         "orr      %[t], %[t2], %[t], lsr %[d]\n\t"
         : [t] "=&r" (t), [t2] "=&r" (t2)
         : [a] "r" (x), [b] "r" (y),
           [c] "Mr" ((z) + 1), [d] "Mr" (31 - (z)));
    return t;
}

#else

static inline int32_t FRACMUL(int32_t x, int32_t y)
{
    return (int32_t) (((int64_t)x * y) >> 31);
}

static inline int32_t FRACMUL_SHL(int32_t x, int32_t y, int z)
{
    return (int32_t) (((int64_t)x * y) >> (31 - z));
}

#endif

#endif