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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; int8_t i, j;
uint8_t carry = 0; uint8_t carry = 0;
uint8_t is_neg; uint8_t is_neg;
int16_t new_exponent;
//initialize values //initialize values
copy_decn(&tmp, x); copy_decn(&tmp, x);
set_dec80_zero(&acc_tmp); set_dec80_zero(&acc_tmp);
//normalize //normalize
remove_leading_zeros(acc); remove_leading_zeros(acc);
remove_leading_zeros(&tmp); remove_leading_zeros(&tmp);
//calculate new exponent //store new sign
if ((acc->exponent & 0x8000) ^ (tmp.exponent & 0x8000)){ //signs differ if ((acc->exponent & 0x8000) ^ (tmp.exponent & 0x8000)){ //signs differ
is_neg = 1; is_neg = 1;
} else { } else {
is_neg = 0; is_neg = 0;
} }
acc_tmp.exponent = get_exponent(acc) + get_exponent(&tmp); //calculate new exponent
if (is_neg){ new_exponent = get_exponent(acc) + get_exponent(&tmp);
acc_tmp.exponent |= 0x8000; #ifdef DEBUG_MULT
} else { printf("\n new exponent: %d:", new_exponent);
acc_tmp.exponent &= 0x7fff; #endif
}
//do multiply //do multiply
for (i = DEC80_NUM_LSU - 1; i >= 0; i--){ for (i = DEC80_NUM_LSU - 1; i >= 0; i--){
//partial product //partial product
@ -643,14 +643,35 @@ void mult_decn(dec80* acc, const dec80* x){
} }
printf("\ncarry:%d", carry); printf("\ncarry:%d", carry);
#endif #endif
if (i != 0){ //handle last carry separately later, no final shift
//shift //shift
shift_right(&acc_tmp); shift_right(&acc_tmp);
shift_right(&acc_tmp); shift_right(&acc_tmp);
//add back carry to MSdigit100 //add back carry to MSdigit100
acc_tmp.lsu[0] = carry; //was 0 from shift 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 back to acc
copy_decn(acc, &acc_tmp); copy_decn(acc, &acc_tmp);
//normalize
remove_leading_zeros(acc);
}
} }
//buf should hold at least 18 + 4 + 5 + 1 = 28 //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); dec80_to_str(buf, &diff);
printf("\n : %s\n\n", buf); 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; return 0;
} }