mathevrc.c

EVRC是用于高通公司的语音编码

 *
 *     INPUTS:
 *
 *       none
 *
 *
 *     OUTPUTS:             none
 *
 *     RETURN VALUE:        value of datum about the be lost (usually the 
 *                          temporary saturation state)
 *
 *     KEYWORDS: saturation, limit, overflow
 *
 ***************************************************************************/

int popOverflow(void)
{
	int i;
	i = giOverflow;
	giOverflow = giOldOverflow;
	return (i);
}

/***************************************************************************
 *
 *   FUNCTION NAME: round
 *
 *   PURPOSE:
 *
 *     Round the 32 bit Longword into a 16 bit shortword with saturation.
 *
 *   INPUTS:
 *
 *     L_var1
 *                     32 bit long signed integer (Longword) whose value
 *                     falls in the range
 *                     0x8000 0000 <= L_var1 <= 0x7fff ffff.
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     swOut
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range
 *                     0xffff 8000 <= swOut <= 0x0000 7fff.
 *
 *   IMPLEMENTATION:
 *
 *     Perform a two's complement round on the input Longword with
 *     saturation.
 *
 *     This is equivalent to adding 0x0000 8000 to the input.  The
 *     result may overflow due to the add.  If so, the result is
 *     saturated.  The 32 bit rounded number is then shifted down
 *     16 bits and returned as a Shortword.
 *
 *
 *   KEYWORDS: round
 *
 *************************************************************************/

Shortword round32(Longword L_var1)
{
	Longword L_Prod;

    OP_COUNT(1);

	L_Prod = L_add(L_var1, 0x00008000L);	/* round MSP */
    OP_COUNT(-3);
    return (extract_h(L_Prod));
}

/****************************************************************************
 *
 *     FUNCTION NAME: set overflow
 *
 *     PURPOSE:
 *
 *        Clear the overflow flag
 *
 *     INPUTS:
 *
 *       none
 *
 *
 *     OUTPUTS:             global overflow flag is cleared
 *                          previous value stored in giOldOverflow
 *
 *     RETURN VALUE:        previous value of overflow
 *                          
 *
 *     KEYWORDS: saturation, limit, overflow
 *
 ***************************************************************************/

int setOverflow(void)
{

	giOldOverflow = giOverflow;
	giOverflow = 1;
	return (giOldOverflow);
}

/***************************************************************************
 *
 *   FUNCTION NAME: shift_r
 *
 *   PURPOSE:
 *
 *     Shift and round.  Perform a shift right. After shifting, use
 *     the last bit shifted out of the LSB to round the result up
 *     or down.
 *
 *   INPUTS:
 *
 *     var1
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range 0xffff 8000 <= var1 <= 0x0000 7fff.
 *     var2
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range 0xffff 8000 <= var2 <= 0x0000 7fff.
 *
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     swOut
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range
 *                     0xffff 8000 <= swOut <= 0x0000 7fff.
 *
 *
 *   IMPLEMENTATION:
 *
 *     Shift and round.  Perform a shift right. After shifting, use
 *     the last bit shifted out of the LSB to round the result up
 *     or down.
 *
 *     If var2 is positive perform a arithmetic left shift
 *     with saturation (see shl() above).
 *
 *     If var2 is zero simply return var1.
 *
 *     If var2 is negative perform a arithmetic right shift (shr)
 *     of var1 by (-var2)+1.  Add the LS bit of the result to var1
 *     shifted right (shr) by -var2.
 *
 *     Note that there is no constraint on var2, so if var2 is
 *     -0xffff 8000 then -var2 is 0x0000 8000, not 0x0000 7fff.
 *     This is the reason the shl function is used.
 *
 *
 *   KEYWORDS:
 *
 *************************************************************************/

Shortword shift_r(Shortword var1, Shortword var2)
{
	Shortword swOut, swRnd;

    OP_COUNT(2);

	if (var2 >= 0)
    {
        swOut = shl(var1, var2);    OP_COUNT(-1);
    }
	else
	{
		/* right shift */
		if (var2 < -15)
		{
			swOut = 0;
		}
		else
		{
            swRnd = shl(var1, var2 + 1) & 0x1;      OP_COUNT(-1);
            swOut = add(shl(var1, var2), swRnd);    OP_COUNT(-2);
		}
	}
	return (swOut);
}

/***************************************************************************
 *
 *   FUNCTION NAME: shl
 *
 *   PURPOSE:
 *
 *     Arithmetically shift the input left by var2.
 *
 *
 *   INPUTS:
 *
 *     var1
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range 0xffff 8000 <= var1 <= 0x0000 7fff.
 *     var2
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range 0xffff 8000 <= var2 <= 0x0000 7fff.
 *
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     swOut
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range
 *                     0xffff 8000 <= swOut <= 0x0000 7fff.
 *
 *   IMPLEMENTATION:
 *
 *     If Arithmetically shift the input left by var2.  If var2 is
 *     negative then an arithmetic shift right (shr) of var1 by
 *     -var2 is performed.  See description of shr for details.
 *     When an arithmetic shift left is performed the var2 LS bits
 *     are zero filled.
 *
 *     The only exception is if the left shift causes an overflow
 *     or underflow.  In this case the LS bits are not modified.
 *     The number returned is 0x8000 in the case of an underflow or
 *     0x7fff in the case of an overflow.
 *
 *     The shl is equivalent to the Full-Rate GSM "<< n" operation.
 *     Note that ANSI-C does not guarantee operation of the C ">>"
 *     or "<<" operator for negative numbers - it is not specified
 *     whether this shift is an arithmetic or logical shift.
 *
 *   KEYWORDS: asl, arithmetic shift left, shift
 *
 *************************************************************************/

Shortword shl(Shortword var1, Shortword var2)
{
	Shortword swOut;
	Longword L_Out;

    OP_COUNT(1);

	if (var2 == 0 || var1 == 0)
	{
		swOut = var1;
	}
	else if (var2 < 0)
	{
		/* perform a right shift */
        /*-----------------------*/
		if (var2 <= -15)
		{
			if (var1 < 0)
				swOut = (Shortword) 0xffff;
			else
				swOut = 0x0;
		}
		else
        {
            swOut = shr(var1, -var2);   OP_COUNT(-1);
        }
	}
	else
	{
		/* var2 > 0 */
		if (var2 >= 15)
		{
			/* saturate */
			if (var1 > 0)
				swOut = SW_MAX;
			else
				swOut = SW_MIN;
			giOverflow = 1;
		}
		else
		{
			L_Out = (Longword) var1 *(1 << var2);

			swOut = (Shortword) L_Out;	/* copy low portion to swOut, overflow
										 * could have hpnd */
			if (swOut != L_Out)
			{
				/* overflow  */
				if (var1 > 0)
					swOut = SW_MAX;		/* saturate */
				else
					swOut = SW_MIN;		/* saturate */
				giOverflow = 1;
			}
		}
	}
	return (swOut);
}

/***************************************************************************
 *
 *   FUNCTION NAME: shr
 *
 *   PURPOSE:
 *
 *     Arithmetic shift right (or left).
 *     Arithmetically shift the input right by var2.   If var2 is
 *     negative then an arithmetic shift left (shl) of var1 by
 *     -var2 is performed.
 *
 *   INPUTS:
 *
 *     var1
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range 0xffff 8000 <= var1 <= 0x0000 7fff.
 *     var2
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range 0xffff 8000 <= var2 <= 0x0000 7fff.
 *
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     swOut
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range
 *                     0xffff 8000 <= swOut <= 0x0000 7fff.
 *
 *   IMPLEMENTATION:
 *
 *     Arithmetically shift the input right by var2.  This
 *     operation maintains the sign of the input number. If var2 is
 *     negative then an arithmetic shift left (shl) of var1 by
 *     -var2 is performed.  See description of shl for details.
 *
 *     Equivalent to the Full-Rate GSM ">> n" operation.  Note that
 *     ANSI-C does not guarantee operation of the C ">>" or "<<"
 *     operator for negative numbers.
 *
 *   KEYWORDS: shift, arithmetic shift right,
 *
 *************************************************************************/

Shortword shr(Shortword var1, Shortword var2)
{
	Shortword swMask, swOut;

    OP_COUNT(1);

	if (var2 == 0 || var1 == 0)
		swOut = var1;

	else if (var2 < 0)
	{
		/* perform an arithmetic left shift */
        /*----------------------------------*/
		if (var2 <= -15)
		{
			/* saturate */
			if (var1 > 0)
				swOut = SW_MAX;
			else
				swOut = SW_MIN;
			giOverflow = 1;
		}
		else
        {
            swOut = shl(var1, -var2);       OP_COUNT(-1);
        }
	}
	else
	{
		/* positive shift count */
        /*----------------------*/

		if (var2 >= 15)
		{
			if (var1 < 0)
				swOut = (Shortword) 0xffff;
			else
				swOut = 0x0;
		}
		else
		{
			/* take care of sign extension */
            /*-----------------------------*/

			swMask = 0;
			if (var1 < 0)
			{
				swMask = ~swMask << (16 - var2);
			}

			var1 >>= var2;
			swOut = swMask | var1;
		}
	}
	return (swOut);
}

/***************************************************************************
 *
 *   FUNCTION NAME: sub
 *
 *   PURPOSE:
 *
 *     Perform the subtraction of the two 16 bit input variable with
 *     saturation.
 *
 *   INPUTS:
 *
 *     var1
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range 0xffff 8000 <= var1 <= 0x0000 7fff.
 *     var2
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range 0xffff 8000 <= var2 <= 0x0000 7fff.
 *
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     swOut
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range
 *                     0xffff 8000 <= swOut <= 0x0000 7fff.
 *
 *   IMPLEMENTATION:
 *
 *     Perform the subtraction of the two 16 bit input variable with
 *     saturation.
 *
 *     swOut = var1 - var2
 *
 *     swOut is set to 0x7fff if the operation results in an
 *     overflow.  swOut is set to 0x8000 if the operation results
 *     in an underflow.
 *
 *   KEYWORDS: sub, subtraction
 *
 *************************************************************************/
Shortword sub(Shortword var1, Shortword var2)
{
	Longword L_diff;
	Shortword swOut;

    OP_COUNT(1);

	L_diff = (Longword) var1 - var2;
	swOut = saturate(L_diff);

	return (swOut);
}