mathadv.c

EVRC是用于高通公司的语音编码

	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:
 *
 *     Longword
 *                     output
 *
 *   DESCRIPTION:
 *
 *     log(x) = log(2) * log2(x)
 *            = 0.693147 * log2(x)
 *
 *     log2(x) = 4.0 * (-.3372223*x*x + .9981958*x -.6626105)
 *                           c0            c1          c2   (includes sign)
 *
 *************************************************************************/

Longword fnLog(Longword L_Input)
{

	static Shortword
	    Scale = 22713;			/* 0.693147 = log(2) */
	Longword LwIn;

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

	/* 0.693147*log2(x) */
	/* ---------------- */

	LwIn = fnLog2(L_Input);
	LwIn = L_mpy_ls(LwIn, Scale);

	return (LwIn);
}

/***************************************************************************
 *
 *   FUNCTION NAME: fnLog10
 *
 *   PURPOSE:
 *     The purpose of this function is to take the log base 10 of input and
 *     divide by 32 and return; i.e. output = log10(input)/32
 *
 *   INPUTS:
 *
 *     L_Input
 *                     input
 *
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     Longword
 *                     output
 *
 *   DESCRIPTION:
 *
 *     log10(x) = log10(2) * log2(x)
 *              = 0.30103  * log2(x)
 *
 *     log2(x) = 4.0 * (-.3372223*x*x + .9981958*x -.6626105)
 *                           c0            c1          c2   (includes sign)
 *
 *************************************************************************/

Longword fnLog10(Longword L_Input)
{

	static Shortword
	    Scale = 9864;			/* 0.30103 = log10(2) */
	Longword LwIn;

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

	/* 0.30103*log2(x) */
	/* ------------------- */

	LwIn = fnLog2(L_Input);
	LwIn = L_mpy_ls(LwIn, Scale);

	return (LwIn);
}

/***************************************************************************
 *
 *   FUNCTION NAME: fnExp2
 *
 *   PURPOSE:
 *     The purpose of this function is to implement a base two exponential
 *     2**(32*x) by polynomial approximation
 *
 *
 *   INPUTS:
 *
 *     L_Input
 *                     unnormalized input exponent (input range constrained
 *                     to be < 0)
 *
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     LwIn
 *                     exponential output
 *
 *   DESCRIPTION:
 *
 *     polynomial approximation is used for the generation of the exponential
 *
 *     2**(32*X) = 0.1713425*X*X + 0.6674432*X + 0.9979554
 *                     c2              c1            c0
 *
 *************************************************************************/

Longword fnExp2(Longword L_Input)
{

/*_________________________________________________________________________
 |                                                                         |
 |                           Local Static Variables                        |
 |_________________________________________________________________________|
*/
	static Shortword pswPCoefE[3] =
	{							/* c2,   c1,    c0 */
		0x15ef, 0x556f, 0x7fbd
	};

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

	Shortword swTemp1, swTemp2, swTemp3, swTemp4;
	Longword LwIn;

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

	/* initialize */
	/* ---------- */

	swTemp3 = 0x0020;

	/* determine normlization shift count */
	/* ---------------------------------- */

	swTemp1 = extract_h(L_Input);
	LwIn = L_mult(swTemp1, swTemp3);
	swTemp2 = extract_h(LwIn);

	/* determine un-normalized shift count */
	/* ----------------------------------- */

	swTemp3 = -0x0001;
	swTemp4 = sub(swTemp3, swTemp2);

	/* normalize input */
	/* --------------- */

	LwIn = LwIn & 0xffff;
	LwIn = L_add(LwIn, L_deposit_h(swTemp3));

	LwIn = L_shr(LwIn, 1);
	swTemp1 = extract_l(LwIn);

	/* calculate x*x*c2 */
	/* ---------------- */

	swTemp2 = mult_r(swTemp1, swTemp1);
	LwIn = L_mult(swTemp2, pswPCoefE[0]);

	/* calculate x*x*c2 + x*c1 */
	/* ----------------------- */

	LwIn = L_mac(LwIn, swTemp1, pswPCoefE[1]);

	/* calculate x*x*c2 + x*c1 + c0 */
	/* --------------------------- */

	LwIn = L_add(LwIn, L_deposit_h(pswPCoefE[2]));

	/* un-normalize exponent if its requires it */
	/* ---------------------------------------- */

	if (swTemp4 > 0)
	{
		LwIn = L_shr(LwIn, swTemp4);
	}

	/* return result */
	/* ------------- */

	return (LwIn);
}

/***************************************************************************
 *
 *   FUNCTION NAME: fnExp10
 *
 *   PURPOSE:
 *     The purpose of this function is to implement a base ten exponential
 *     10**(32*x) by polynomial approximation
 *
 *
 *   INPUTS:
 *
 *     L_Input
 *                     unnormalized input exponent (input range constrained
 *                     to be < 0)
 *
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     LwIn
 *                     exponential output
 *
 *   DESCRIPTION:
 *
 *     polynomial approximation is used for the generation of the exponential
 *
 *     10**(32*X) = 2**((32*X) / log10(2))
 *                = 2**((32*X) / 0.30103)
 *
 *     2**(32*X) = 0.1713425*X*X + 0.6674432*X + 0.9979554
 *                     c2              c1            c0
 *
 *************************************************************************/

Longword fnExp10(Longword L_Input)
{

/*_________________________________________________________________________
 |                                                                         |
 |                           Local Static Variables                        |
 |_________________________________________________________________________|
*/
	static Shortword
	    InvScale = 27213;		/* (1/log10(2))/4 */

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

	Longword LwIn;

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

	LwIn = L_mpy_ls(L_Input, InvScale);
	LwIn = L_shl(LwIn, 2);
	LwIn = fnExp2(LwIn);

	/* return result */
	/* ------------- */

	return (LwIn);
}