assembly.h

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/**************************************************************************************
 * Fixed-point MP3 decoder
 * Jon Recker (jrecker@real.com), Ken Cooke (kenc@real.com)
 * June 2003
 *
 * assembly.h - assembly language functions and prototypes for supported platforms
 *
 * - inline rountines with access to 64-bit multiply results 
 * - x86 (_WIN32) and ARM (ARM_ADS, _WIN32_WCE) versions included
 * - some inline functions are mix of asm and C for speed
 * - some functions are in native asm files, so only the prototype is given here
 *
 * MULSHIFT32(x, y)    signed multiply of two 32-bit integers (x and y), returns top 32 bits of 64-bit result
 * FASTABS(x)          branchless absolute value of signed integer x
 * CLZ(x)              count leading zeros in x
 * MADD64(sum, x, y)   (Windows only) sum [64-bit] += x [32-bit] * y [32-bit]
 * SHL64(sum, x, y)    (Windows only) 64-bit left shift using __int64
 * SAR64(sum, x, y)    (Windows only) 64-bit right shift using __int64
 */

#ifndef _ASSEMBLY_H
#define _ASSEMBLY_H

#if (defined _WIN32 && !defined _WIN32_WCE) || (defined __WINS__ && defined _SYMBIAN) || defined(_OPENWAVE_SIMULATOR) || defined(WINCE_EMULATOR)    /* Symbian emulator for Ix86 */

#pragma warning( disable : 4035 )       /* complains about inline asm not returning a value */

static __inline int MULSHIFT32(int x, int y)    
{
    __asm {
                mov             eax, x
            imul        y
            mov         eax, edx
        }
}

static __inline int FASTABS(int x) 
{
        int sign;

        sign = x >> (sizeof(int) * 8 - 1);
        x ^= sign;
        x -= sign;

        return x;
}

static __inline int CLZ(int x)
{
        int numZeros;

        if (!x)
                return (sizeof(int) * 8);

        numZeros = 0;
        while (!(x & 0x80000000)) {
                numZeros++;
                x <<= 1;
        } 

        return numZeros;
}

/* MADD64, SHL64, SAR64:
 * write in assembly to avoid dependency on run-time lib for 64-bit shifts, muls
 *  (sometimes compiler thunks to function calls instead of code generating)
 * required for Symbian emulator
 */
static __inline __int64 MADD64(__int64 sum, int x, int y)
{
        unsigned int sumLo = ((unsigned int *)&sum)[0];
        int sumHi = ((int *)&sum)[1];

        __asm {
                mov             eax, x
                imul    y
                add             eax, sumLo
                adc             edx, sumHi
        }

        /* equivalent to return (sum + ((__int64)x * y)); */
}

static __inline __int64 SHL64(__int64 x, int n)
{
        unsigned int xLo = ((unsigned int *)&x)[0];
        int xHi = ((int *)&x)[1];
        unsigned char nb = (unsigned char)n;

        if (n < 32) {
                __asm {
                        mov             edx, xHi
                        mov             eax, xLo
                        mov             cl, nb
                        shld    edx, eax, cl
                        shl     eax, cl
                }
        } else if (n < 64) {
                /* shl masks cl to 0x1f */
                __asm {
                        mov             edx, xLo
                        mov             cl, nb
                        xor     eax, eax
                        shl     edx, cl
                }
        } else {
                __asm {
                        xor             edx, edx
                        xor             eax, eax
                }
        }
}

static __inline __int64 SAR64(__int64 x, int n)
{
        unsigned int xLo = ((unsigned int *)&x)[0];
        int xHi = ((int *)&x)[1];
        unsigned char nb = (unsigned char)n;

        if (n < 32) {
                __asm {
                        mov             edx, xHi
                        mov             eax, xLo
                        mov             cl, nb
                        shrd    eax, edx, cl
                        sar             edx, cl
                }
        } else if (n < 64) {
                /* sar masks cl to 0x1f */
                __asm {
                        mov             edx, xHi
                        mov             eax, xHi
                        mov             cl, nb
                        sar             edx, 31
                        sar             eax, cl
                }
        } else {
                __asm {
                        sar             xHi, 31
                        mov             eax, xHi
                        mov             edx, xHi
                }
        }
}

#elif (defined _WIN32) && (defined _WIN32_WCE)

/* use asm function for now (EVC++ 3.0 does horrible job compiling __int64 version) */
#define MULSHIFT32      xmp3_MULSHIFT32
int MULSHIFT32(int x, int y);

static __inline int FASTABS(int x) 
{
        int sign;

        sign = x >> (sizeof(int) * 8 - 1);
        x ^= sign;
        x -= sign;

        return x;
}

static __inline int CLZ(int x)
{
        int numZeros;

        if (!x)
                return (sizeof(int) * 8);

        numZeros = 0;
        while (!(x & 0x80000000)) {
                numZeros++;
                x <<= 1;
        } 

        return numZeros;
}

#elif defined ARM_ADS

static __inline int MULSHIFT32(int x, int y)
{
    /* important rules for smull RdLo, RdHi, Rm, Rs:
     *     RdHi and Rm can't be the same register
     *     RdLo and Rm can't be the same register
     *     RdHi and RdLo can't be the same register
     * Note: Rs determines early termination (leading sign bits) so if you want to specify
     *   which operand is Rs, put it in the SECOND argument (y)
         * For inline assembly, x and y are not assumed to be R0, R1 so it shouldn't matter
         *   which one is returned. (If this were a function call, returning y (R1) would 
         *   require an extra "mov r0, r1")
     */
    int zlow;
    __asm {
        smull zlow,y,x,y
        }

    return y;
}

static __inline int FASTABS(int x) 
{
        int t;

        __asm {
                eor     t, x, x, asr #31
                sub     t, t, x, asr #31
        }

        return t;
}

static __inline int CLZ(int x)
{
        int numZeros;

        if (!x)
                return (sizeof(int) * 8);

        numZeros = 0;
        while (!(x & 0x80000000)) {
                numZeros++;
                x <<= 1;
        } 

        return numZeros;
}

#elif defined(__GNUC__) && defined(__arm__)

static __inline int MULSHIFT32(int x, int y)
{
    /* important rules for smull RdLo, RdHi, Rm, Rs:
     *     RdHi and Rm can't be the same register
     *     RdLo and Rm can't be the same register
     *     RdHi and RdLo can't be the same register
     * Note: Rs determines early termination (leading sign bits) so if you want to specify
     *   which operand is Rs, put it in the SECOND argument (y)
         * For inline assembly, x and y are not assumed to be R0, R1 so it shouldn't matter
         *   which one is returned. (If this were a function call, returning y (R1) would 
         *   require an extra "mov r0, r1")
     */
    int zlow;
    __asm__ volatile ("smull %0,%1,%2,%3" : "=&r" (zlow), "=r" (y) : "r" (x), "1" (y)) ;

    return y;
}

static __inline int FASTABS(int x) 
{
        int t = 0;

        __asm__ volatile (
                "eor %0,%2,%2, asr #31;"
                "sub %0,%1,%2, asr #31;"
                : "=&r" (t) 
                : "0" (t), "r" (x)
         );

        return t;
}

static __inline int CLZ(int x)
{
        int numZeros;

        if (!x)
                return (sizeof(int) * 8);

        numZeros = 0;
        while (!(x & 0x80000000)) {
                numZeros++;
                x <<= 1;
        } 

        return numZeros;
}

#else

#error Unsupported platform in assembly.h

#endif  /* platforms */

#endif /* _ASSEMBLY_H */