basic_op.c

以上是标准的G.722源代码

    if (var2 < 0)
    {
        neg_var2 = negate(var2);
        var_out = shr (var1, neg_var2);

    }
    else
    {
        result = (Word32) var1 *((Word32) 1 << var2);

        if ((var2 > 15 && var1 != 0) || (result != (Word32) ((Word16) result)))
        {
            Overflow = 1;
            var_out = (var1 > 0) ? MAX_16 : MIN_16;
        }
        else
        {
            var_out = extract_l (result);
        }
    }
    return (var_out);
}

/*___________________________________________________________________________
 |                                                                           |
 |   Function Name : shr                                                     |
 |                                                                           |
 |   Purpose :                                                               |
 |                                                                           |
 |   Arithmetically shift the 16 bit input var1 right var2 positions with    |
 |   sign extension. If var2 is negative, arithmetically shift var1 left by  |
 |   -var2 with sign extension. Saturate the result in case of underflows or |
 |   overflows.                                                              |
 |                                                                           |
 |   Complexity weight : 1                                                   |
 |                                                                           |
 |   Inputs :                                                                |
 |                                                                           |
 |    var1                                                                   |
 |             16 bit short signed integer (Word16) whose value falls in the |
 |             range : 0xffff 8000 <= var1 <= 0x0000 7fff.                   |
 |                                                                           |
 |    var2                                                                   |
 |             16 bit short signed integer (Word16) whose value falls in the |
 |             range : 0xffff 8000 <= var1 <= 0x0000 7fff.                   |
 |                                                                           |
 |   Outputs :                                                               |
 |                                                                           |
 |    none                                                                   |
 |                                                                           |
 |   Return Value :                                                          |
 |                                                                           |
 |    var_out                                                                |
 |             16 bit short signed integer (Word16) whose value falls in the |
 |             range : 0xffff 8000 <= var_out <= 0x0000 7fff.                |
 |___________________________________________________________________________|
*/  

Word16 shr (Word16 var1, Word16 var2)
{
    Word16 var_out;
    Word16 neg_var2;

    if (var2 < 0)
    {
        neg_var2 = negate(var2);
        var_out = shl (var1, neg_var2);
    }
    else
    {
        if (var2 >= 15)
        {
            var_out = (var1 < 0) ? -1 : 0;
        }
        else
        {
            if (var1 < 0)
            {
                var_out = ~((~var1) >> var2);
            }
            else
            {
                var_out = var1 >> var2;
            }
        }
    }

    return (var_out);
}

/*___________________________________________________________________________
 |                                                                           |
 |   Function Name : mult                                                    |
 |                                                                           |
 |   Purpose :                                                               |
 |                                                                           |
 |    Performs the multiplication of var1 by var2 and gives a 16 bit result  |
 |    which is scaled i.e.:                                                  |
 |             mult(var1,var2) = extract_l(L_shr((var1 times var2),15)) and  |
 |             mult(-32768,-32768) = 32767.                                  |
 |                                                                           |
 |   Complexity weight : 1                                                   |
 |                                                                           |
 |   Inputs :                                                                |
 |                                                                           |
 |    var1                                                                   |
 |             16 bit short signed integer (Word16) whose value falls in the |
 |             range : 0xffff 8000 <= var1 <= 0x0000 7fff.                   |
 |                                                                           |
 |    var2                                                                   |
 |             16 bit short signed integer (Word16) whose value falls in the |
 |             range : 0xffff 8000 <= var1 <= 0x0000 7fff.                   |
 |                                                                           |
 |   Outputs :                                                               |
 |                                                                           |
 |    none                                                                   |
 |                                                                           |
 |   Return Value :                                                          |
 |                                                                           |
 |    var_out                                                                |
 |             16 bit short signed integer (Word16) whose value falls in the |
 |             range : 0xffff 8000 <= var_out <= 0x0000 7fff.                |
 |___________________________________________________________________________|
*/  

Word16 mult (Word16 var1, Word16 var2)
{
    Word16 var_out;
    Word32 L_product;

    L_product = (Word32) var1 *(Word32) var2;

    L_product = (L_product & (Word32) 0xffff8000L) >> 15;

    if (L_product & (Word32) 0x00010000L)
        L_product = L_product | (Word32) 0xffff0000L;

    var_out = saturate (L_product);
    return (var_out);
}

/*___________________________________________________________________________
 |                                                                           |
 |   Function Name : L_mult                                                  |
 |                                                                           |
 |   Purpose :                                                               |
 |                                                                           |
 |   L_mult is the 32 bit result of the multiplication of var1 times var2    |
 |   with one shift left i.e.:                                               |
 |        L_mult(var1,var2) = L_shl((var1 times var2),1) and                   |
 |        L_mult(-32768,-32768) = 2147483647.                                |
 |                                                                           |
 |   Complexity weight : 1                                                   |
 |                                                                           |
 |   Inputs :                                                                |
 |                                                                           |
 |    var1                                                                   |
 |             16 bit short signed integer (Word16) whose value falls in the |
 |             range : 0xffff 8000 <= var1 <= 0x0000 7fff.                   |
 |                                                                           |
 |    var2                                                                   |
 |             16 bit short signed integer (Word16) whose value falls in the |
 |             range : 0xffff 8000 <= var1 <= 0x0000 7fff.                   |
 |                                                                           |
 |   Outputs :                                                               |
 |                                                                           |
 |    none                                                                   |
 |                                                                           |
 |   Return Value :                                                          |
 |                                                                           |
 |    L_var_out                                                              |
 |             32 bit long signed integer (Word32) whose value falls in the  |
 |             range : 0x8000 0000 <= L_var_out <= 0x7fff ffff.              |
 |___________________________________________________________________________|
*/  

Word32 L_mult (Word16 var1, Word16 var2)
{
    Word32 L_var_out;

    L_var_out = (Word32) var1 *(Word32) var2;

    if (L_var_out != (Word32) 0x40000000L)
    {
        L_var_out *= 2;
    }
    else
    {
        Overflow = 1;
        L_var_out = MAX_32;
    }

    return (L_var_out);
}

/*___________________________________________________________________________
 |                                                                           |
 |   Function Name : Q0_mult                                                  |
 |                                                                           |
 |   Purpose :                                                               |
 |                                                                           |
 |   L_mult is the 32 bit result of the multiplication of var1 times var2    |
 |   without any shift i.e.:                                               |
 |        Q0_mult(var1,var2) = (var1 times var2)                   |
 |        Q0_mult(-32768,-32768) = 2147483647.                                |
 |                                                                           |
 |   Complexity weight : 1                                                   |
 |                                                                           |
 |   Inputs :                                                                |
 |                                                                           |
 |    var1                                                                   |
 |             16 bit short signed integer (Word16) whose value falls in the |
 |             range : 0xffff 8000 <= var1 <= 0x0000 7fff.                   |
 |                                                                           |
 |    var2                                                                   |
 |             16 bit short signed integer (Word16) whose value falls in the |
 |             range : 0xffff 8000 <= var1 <= 0x0000 7fff.                   |
 |                                                                           |
 |   Outputs :                                                               |
 |                                                                           |
 |    none                                                                   |
 |                                                                           |
 |   Return Value :                                                          |
 |                                                                           |
 |    L_var_out                                                              |
 |             32 bit long signed integer (Word32) whose value falls in the  |
 |             range : 0x8000 0000 <= L_var_out <= 0x7fff ffff.              |
 |___________________________________________________________________________|
*/  

Word32 Q0_mult (Word16 var1, Word16 var2)
{
    Word32 L_var_out;

    L_var_out = (Word32) var1 *(Word32) var2;