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bugfixes for multiply

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This commit is contained in:
Jeff Wang 2019-03-27 05:19:57 -04:00
parent 0ba2ca7710
commit 116b6ed2e6
2 changed files with 39 additions and 7 deletions
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35
src/decn/decn.c
View File

@ -597,24 +597,24 @@ void mult_decn(dec80* acc, const dec80* x){
int8_t i, j;
uint8_t carry = 0;
uint8_t is_neg;
int16_t new_exponent;
//initialize values
copy_decn(&tmp, x);
set_dec80_zero(&acc_tmp);
//normalize
remove_leading_zeros(acc);
remove_leading_zeros(&tmp);
//calculate new exponent
//store new sign
if ((acc->exponent & 0x8000) ^ (tmp.exponent & 0x8000)){ //signs differ
is_neg = 1;
} else {
is_neg = 0;
}
acc_tmp.exponent = get_exponent(acc) + get_exponent(&tmp);
if (is_neg){
acc_tmp.exponent |= 0x8000;
} else {
acc_tmp.exponent &= 0x7fff;
}
//calculate new exponent
new_exponent = get_exponent(acc) + get_exponent(&tmp);
#ifdef DEBUG_MULT
printf("\n new exponent: %d:", new_exponent);
#endif
//do multiply
for (i = DEC80_NUM_LSU - 1; i >= 0; i--){
//partial product
@ -643,14 +643,35 @@ void mult_decn(dec80* acc, const dec80* x){
}
printf("\ncarry:%d", carry);
#endif
if (i != 0){ //handle last carry separately later, no final shift
//shift
shift_right(&acc_tmp);
shift_right(&acc_tmp);
//add back carry to MSdigit100
acc_tmp.lsu[0] = carry; //was 0 from shift
}
}
//handle last carry
if (carry > 10){
//shift
shift_right(&acc_tmp);
shift_right(&acc_tmp);
new_exponent += 1;
//add back carry to MSdigit100
acc_tmp.lsu[0] = carry; //was 0 from shift
} else if (carry > 0){
//shift
shift_right(&acc_tmp);
//add back carry to MSdigit in MSdigit100
acc_tmp.lsu[0] += carry*10;
}
//set new exponent
set_exponent(&acc_tmp, new_exponent, is_neg);
//copy back to acc
copy_decn(acc, &acc_tmp);
//normalize
remove_leading_zeros(acc);
}
}
//buf should hold at least 18 + 4 + 5 + 1 = 28

11
src/decn/decn_test.c
View File

@ -61,6 +61,17 @@ int main(void){
dec80_to_str(buf, &diff);
printf("\n : %s\n\n", buf);
//new acc and b for multiply test
// build_dec80(&acc, "2", 2);
build_dec80(&acc, "92.34567890123456", 2);
build_dec80(&b, "-92.3456789012345678", 1);
dec80_to_str(buf, &acc);
printf(" acc: %s\n", buf);
dec80_to_str(buf, &b);
printf(" b: %s\n", buf);
mult_decn(&acc, &b);
dec80_to_str(buf, &acc);
printf("acc*b: %s\n\n", buf);
return 0;
}