ref: d6185567e2757c9bd74defdfe7f227e59f2d6cd2
dir: /src/libgsm/add.c/
/*
* Copyright 1992 by Jutta Degener and Carsten Bormann, Technische
* Universitaet Berlin. See the accompanying file "COPYRIGHT" for
* details. THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE.
*/
/*
* See private.h for the more commonly used macro versions.
*/
#include <stdio.h>
#include <assert.h>
#include "private.h"
#include "gsm.h"
#define saturate(x) \
((x) < MIN_WORD ? MIN_WORD : (x) > MAX_WORD ? MAX_WORD: (x))
word gsm_add (word a, word b)
{
longword sum = (longword)a + (longword)b;
return saturate(sum);
}
word gsm_sub (word a, word b)
{
longword diff = (longword)a - (longword)b;
return saturate(diff);
}
word gsm_mult (word a, word b)
{
if (a == MIN_WORD && b == MIN_WORD) return MAX_WORD;
else return SASR( (longword)a * (longword)b, 15 );
}
static unsigned char const bitoff[ 256 ] = {
8, 7, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4,
3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
};
word gsm_norm (longword a )
/*
* the number of left shifts needed to normalize the 32 bit
* variable L_var1 for positive values on the interval
*
* with minimum of
* minimum of 1073741824 (01000000000000000000000000000000) and
* maximum of 2147483647 (01111111111111111111111111111111)
*
*
* and for negative values on the interval with
* minimum of -2147483648 (-10000000000000000000000000000000) and
* maximum of -1073741824 ( -1000000000000000000000000000000).
*
* in order to normalize the result, the following
* operation must be done: L_norm_var1 = L_var1 << norm( L_var1 );
*
* (That's 'ffs', only from the left, not the right..)
*/
{
assert(a != 0);
if (a < 0) {
if (a <= -1073741824) return 0;
a = ~a;
}
return a & 0xffff0000
? ( a & 0xff000000
? -1 + bitoff[ 0xFF & (a >> 24) ]
: 7 + bitoff[ 0xFF & (a >> 16) ] )
: ( a & 0xff00
? 15 + bitoff[ 0xFF & (a >> 8) ]
: 23 + bitoff[ 0xFF & a ] );
}
word gsm_asl (word a, int n)
{
if (n >= 16) return 0;
if (n <= -16) return -(a < 0);
if (n < 0) return gsm_asr(a, -n);
return a << n;
}
word gsm_asr (word a, int n)
{
if (n >= 16) return -(a < 0);
if (n <= -16) return 0;
if (n < 0) return a << -n;
return SASR(a, n);
}
/*
* (From p. 46, end of section 4.2.5)
*
* NOTE: The following lines gives [sic] one correct implementation
* of the div(num, denum) arithmetic operation. Compute div
* which is the integer division of num by denum: with denum
* >= num > 0
*/
word gsm_div (word num, word denum)
{
longword L_num = num;
longword L_denum = denum;
word div = 0;
int k = 15;
/* The parameter num sometimes becomes zero.
* Although this is explicitly guarded against in 4.2.5,
* we assume that the result should then be zero as well.
*/
/* assert(num != 0); */
assert(num >= 0 && denum >= num);
if (num == 0)
return 0;
while (k--) {
div <<= 1;
L_num <<= 1;
if (L_num >= L_denum) {
L_num -= L_denum;
div++;
}
}
return div;
}