math_adv.c

完整的EVRC压缩解压缩算法源码,通过C-C++编译后可以运行!

	if (L_num < 0 || L_denom < 0 || L_num > L_denom)
	{
		printf("ERROR: Invalid input into L_divide!\n");
		return (0);
	}

	/* First approximation: 1 / L_denom = 1/extract_h(L_denom) */

	approx = divide_s((Word16) 0x3fff, extract_h(L_denom));

	/* 1/L_denom = approx * (2.0 - L_denom * approx) */

	L_div = L_mpy_ls(L_denom, approx);

	L_div = L_sub((Word32) 0x7fffffffL, L_div);

	L_div = L_mpy_ls(L_div, approx);

	/* L_num * (1/L_denom) */

	L_div = L_mpy_ll(L_num, L_div);
	L_div = L_shl(L_div, 2);

	return (L_div);
}

/***************************************************************************
 *
 *   FUNCTION NAME: sqroot
 *
 *   PURPOSE:
 *
 *     The purpose of this function is to perform a single precision square
 *     root function on a Word32
 *
 *   INPUTS:
 *
 *     L_SqrtIn
 *                     input to square root function
 *
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     swSqrtOut
 *                     output to square root function
 *
 *   DESCRIPTION:
 *
 *      Input assumed to be normalized
 *
 *      The algorithm is based around a six term Taylor expansion :
 *
 *        y^0.5 = (1+x)^0.5
 *             ~= 1 + (x/2) - 0.5*((x/2)^2) + 0.5*((x/2)^3)
 *                - 0.625*((x/2)^4) + 0.875*((x/2)^5)
 *
 *      Max error less than 0.08 % for normalized input ( 0.5 <= x < 1 )
 *
 *************************************************************************/

Word16 sqroot(Word32 L_SqrtIn)
{

/*_________________________________________________________________________
 |                                                                         |
 |                              Local Constants                            |
 |_________________________________________________________________________|
*/

#define    PLUS_HALF          0x40000000L	/* 0.5 */
#define    MINUS_ONE          0x80000000L	/* -1 */
#define    TERM5_MULTIPLER    0x5000	/* 0.625 */
#define    TERM6_MULTIPLER    0x7000	/* 0.875 */

/*_________________________________________________________________________
 |                                                                         |
 |                            Automatic Variables                          |
 |_________________________________________________________________________|
*/

	Word32 L_Temp0, L_Temp1;

	Word16 swTemp, swTemp2, swTemp3, swTemp4, swSqrtOut;

/*_________________________________________________________________________
 |                                                                         |
 |                              Executable Code                            |
 |_________________________________________________________________________|
*/

	/* determine 2nd term x/2 = (y-1)/2 */
	/* -------------------------------- */

	L_Temp1 = L_shr(L_SqrtIn, 1);	/* L_Temp1 = y/2 */
	L_Temp1 = L_sub(L_Temp1, PLUS_HALF);	/* L_Temp1 = (y-1)/2 */
	swTemp = extract_h(L_Temp1);	/* swTemp = x/2 */

	/* add contribution of 2nd term */
	/* ---------------------------- */

	L_Temp1 = L_sub(L_Temp1, MINUS_ONE);	/* L_Temp1 = 1 + x/2 */

	/* determine 3rd term */
	/* ------------------ */

	L_Temp0 = L_msu(0L, swTemp, swTemp);	/* L_Temp0 = -(x/2)^2 */
	swTemp2 = extract_h(L_Temp0);	/* swTemp2 = -(x/2)^2 */
	L_Temp0 = L_shr(L_Temp0, 1);	/* L_Temp0 = -0.5*(x/2)^2 */

	/* add contribution of 3rd term */
	/* ---------------------------- */

	L_Temp0 = L_add(L_Temp1, L_Temp0);	/* L_Temp0 = 1 + x/2 - 0.5*(x/2)^2 */

	/* determine 4rd term */
	/* ------------------ */

	L_Temp1 = L_msu(0L, swTemp, swTemp2);	/* L_Temp1 = (x/2)^3 */
	swTemp3 = extract_h(L_Temp1);	/* swTemp3 = (x/2)^3 */
	L_Temp1 = L_shr(L_Temp1, 1);	/* L_Temp1 = 0.5*(x/2)^3 */

	/* add contribution of 4rd term */
	/* ---------------------------- */

	/* L_Temp1 = 1 + x/2 - 0.5*(x/2)^2 + 0.5*(x/2)^3 */

	L_Temp1 = L_add(L_Temp0, L_Temp1);

	/* determine partial 5th term */
	/* -------------------------- */

	L_Temp0 = L_mult(swTemp, swTemp3);	/* L_Temp0 = (x/2)^4 */
	swTemp4 = round32(L_Temp0);	/* swTemp4 = (x/2)^4 */

	/* determine partial 6th term */
	/* -------------------------- */

	L_Temp0 = L_msu(0L, swTemp2, swTemp3);	/* L_Temp0 = (x/2)^5 */
	swTemp2 = round32(L_Temp0);	/* swTemp2 = (x/2)^5 */

	/* determine 5th term and add its contribution */
	/* ------------------------------------------- */

	/* L_Temp0 = -0.625*(x/2)^4 */

	L_Temp0 = L_msu(0L, TERM5_MULTIPLER, swTemp4);

	/* L_Temp1 = 1 + x/2 - 0.5*(x/2)^2 + 0.5*(x/2)^3 - 0.625*(x/2)^4 */

	L_Temp1 = L_add(L_Temp0, L_Temp1);

	/* determine 6th term and add its contribution */
	/* ------------------------------------------- */

	/* swSqrtOut = 1 + x/2 - 0.5*(x/2)^2 + 0.5*(x/2)^3 */
	/* - 0.625*(x/2)^4 + 0.875*(x/2)^5     */

	swSqrtOut = mac_r(L_Temp1, TERM6_MULTIPLER, swTemp2);

	/* return output */
	/* ------------- */

	return (swSqrtOut);
}

/***************************************************************************
 *
 *   FUNCTION NAME: fnLog2
 *
 *   PURPOSE:
 *     The purpose of this function is to take the log base 2 of input and
 *     divide by 32 and return; i.e. output = log2(input)/32
 *
 *   INPUTS:
 *
 *     L_Input
 *                     input
 *
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     Word32
 *                     output
 *
 *   DESCRIPTION:
 *
 *     log2(x) = 4.0 * (-.3372223*x*x + .9981958*x -.6626105)
 *                           c0            c1          c2   (includes sign)
 *
 *************************************************************************/

Word32 fnLog2(Word32 L_Input)
{

	static Word16
	    swC0 = -0x2b2a, swC1 = 0x7fc5, swC2 = -0x54d0;

	Word16 siShiftCnt, swInSqrd, swIn;
	Word32 LwIn;

/*_________________________________________________________________________
 |                                                                         |
 |                              Executable Code                            |
 |_________________________________________________________________________|
*/

	/* normalize input and store shifts required */
	/* ----------------------------------------- */

	siShiftCnt = norm_l(L_Input);
	LwIn = L_shl(L_Input, siShiftCnt);
	siShiftCnt = add(siShiftCnt, 1);
	siShiftCnt = negate(siShiftCnt);

	/* calculate x*x*c0 */
	/* ---------------- */

	swIn = extract_h(LwIn);
	swInSqrd = mult_r(swIn, swIn);
	LwIn = L_mult(swInSqrd, swC0);

	/* add x*c1 */
	/* --------- */

	LwIn = L_mac(LwIn, swIn, swC1);

	/* add c2 */
	/* ------ */

	LwIn = L_add(LwIn, L_deposit_h(swC2));

	/* apply *(4/32) */
	/* ------------- */

	LwIn = L_shr(LwIn, 3);
	LwIn = LwIn & 0x03ffffff;
	siShiftCnt = shl(siShiftCnt, 10);
	LwIn = L_add(LwIn, L_deposit_h(siShiftCnt));

	/* return log2 */
	/* ----------- */

	return (LwIn);
}

/***************************************************************************
 *
 *   FUNCTION NAME: fnLog
 *
 *   PURPOSE:
 *     The purpose of this function is to take the natural log of input and
 *     divide by 32 and return; i.e. output = log(input)/32
 *
 *   INPUTS:
 *
 *     L_Input
 *                     input
 *
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     Word32
 *                     output
 *
 *   DESCRIPTION:
 *