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multiplication

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This commit is contained in:
Jeff Wang 2019-03-27 03:53:18 -04:00
parent d2faa41dd5
commit 14251c91cb
2 changed files with 65 additions and 0 deletions
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64
src/decn/decn.c
View File

@ -9,12 +9,14 @@
//#define DEBUG
//#define DEBUG_ADD
#define DEBUG_MULT
//#define DEBUG_COMPARE_MAGN
#ifndef DESKTOP
#undef DEBUG
#undef DEBUG_ADD
#undef DEBUG_COMPARE_MAGN
#undef DEBUG_MULT
#endif
#ifdef DESKTOP
@ -587,6 +589,68 @@ void add_decn(dec80* acc, const dec80* x){
}
}
void mult_decn(dec80* acc, const dec80* x){
dec80 tmp; //copy of x
dec80 acc_tmp; //holds sum
int8_t i, j;
uint8_t carry = 0;
uint8_t is_neg;
//initialize values
copy_decn(&tmp, x);
set_dec80_zero(&acc_tmp);
//normalize
remove_leading_zeros(acc);
remove_leading_zeros(&tmp);
//calculate new exponent
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;
}
//do multiply
for (i = DEC80_NUM_LSU - 1; i >= 0; i--){
//partial product
for (j = DEC80_NUM_LSU - 1; j >= 0; j--){
uint16_t digit100 = acc_tmp.lsu[j] + (tmp.lsu[i] * acc->lsu[j]) + carry;
acc_tmp.lsu[j] = digit100 % 100;
carry = digit100 / 100;
assert(carry < 100);
}
#ifdef DEBUG_MULT
printf("\n%d:", i);
printf("\n acc:");
for (j = 0; j < DEC80_NUM_LSU; j++){
printf(" %3d", acc->lsu[j]);
}
printf("\n x:");
for (j = 0; j < DEC80_NUM_LSU; j++){
if (j == i)
printf(" %3d", tmp.lsu[j]);
else
printf(" ");
}
printf("\n acc_tmp:");
for (j = 0; j < DEC80_NUM_LSU; j++){
printf(" %3d", acc_tmp.lsu[j]);
}
printf("\ncarry:%d", carry);
#endif
//shift
shift_right(&acc_tmp);
shift_right(&acc_tmp);
//add back carry to MSdigit100
acc_tmp.lsu[0] = carry; //was 0 from shift
}
//copy back to acc
copy_decn(acc, &acc_tmp);
}
//buf should hold at least 18 + 4 + 5 + 1 = 28
void dec80_to_str(char* buf, const dec80* x){
uint8_t i = 0;

1
src/decn/decn.h
View File

@ -38,6 +38,7 @@ void set_dec80_NaN(dec80* dest);
void negate_decn(dec80* x);
int8_t compare_decn(dec80* a, dec80* b); //a<b: -1, a==b: 0, a>b: 1
void add_decn(dec80* acc, const dec80* x);
void mult_decn(dec80* acc, const dec80* x);
//buf should hold at least 18 + 4 + 5 + 1 = 28
#define DECN_BUF_SIZE 28