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division

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This commit is contained in:
Jeff Wang 2019-03-27 05:23:26 -04:00
parent b3c73cbdb5
commit 4405ee7c8f
3 changed files with 72 additions and 3 deletions
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56
src/decn/decn.c
View File

@ -8,15 +8,17 @@
#include "../utils.h"
//#define DEBUG
//#define DEBUG_ADD
#define DEBUG_MULT
//#define DEBUG_COMPARE_MAGN
//#define DEBUG_ADD
//#define DEBUG_MULT
//#define DEBUG_DIV
#ifndef DESKTOP
#undef DEBUG
#undef DEBUG_ADD
#undef DEBUG_COMPARE_MAGN
#undef DEBUG_ADD
#undef DEBUG_MULT
#undef DEBUG_DIV
#endif
#ifdef DESKTOP
@ -672,6 +674,54 @@ void mult_decn(dec80* acc, const dec80* x){
//normalize
remove_leading_zeros(acc);
}
void div_decn(dec80* acc, const dec80* x){
dec80 tmp; //copy of x, holds current 1/x estimate
dec80 acc_copy; //holds copy of original acc
uint8_t i;
//check divide by zero
if (decn_is_zero(x)){
set_dec80_NaN(acc);
return;
}
//store copy of acc for final multiply by 1/x
copy_decn(&acc_copy, acc);
//get initial estimate for 1/x, by negating exponent, and setting signif. to 1
set_exponent(&tmp, -get_exponent(x), (x->exponent < 0));
tmp.lsu[0] = 10; //1 with implicit point
for (i = 1; i < DEC80_NUM_LSU; i++){
tmp.lsu[i] = 0;
}
copy_decn(acc, &tmp);
//do newton raphson iterations
for (i = 0; i < 20; i++){ //just fix number of iterations for now
#ifdef DEBUG_DIV
char buf[80];
dec80_to_str(buf, &tmp);
printf("%2d: %s\n", i, buf);
#endif
mult_decn(acc, x);
#ifdef DEBUG_DIV
dec80_to_str(buf, acc);
printf(" %20s: %s\n", "recip*x", buf);
#endif
negate_decn(acc);
add_decn(acc, &DECN_1);
#ifdef DEBUG_DIV
dec80_to_str(buf, acc);
printf(" %20s: %s\n", "(1-recip*x)", buf);
#endif
mult_decn(acc, &tmp);
#ifdef DEBUG_DIV
dec80_to_str(buf, acc);
printf(" %20s: %s\n", "recip * (1-recip*x)", buf);
#endif
add_decn(acc, &tmp);
//new_est(acc) = recip + (1 - recip*x)*recip, where tmp is current recip estimate
copy_decn(&tmp, acc);
}
//acc now holds 1/x, multiply by original acc to complete division
mult_decn(acc, &acc_copy);
}
//buf should hold at least 18 + 4 + 5 + 1 = 28

7
src/decn/decn.h
View File

@ -23,6 +23,12 @@ typedef struct {
//implicit decimal point between (lsu[0]/10) and (lsu[0]%10)
} dec80;
//1 constant
static const dec80 DECN_1 = {
0,
{10, 0}
};
//remove sign bit, and return 15 bit exponent sign-extended to 16 bits
int16_t get_exponent(const dec80* x);
@ -39,6 +45,7 @@ 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);
void div_decn(dec80* acc, const dec80* x);
//buf should hold at least 18 + 4 + 5 + 1 = 28
#define DECN_BUF_SIZE 28

12
src/decn/decn_test.c
View File

@ -73,5 +73,17 @@ int main(void){
dec80_to_str(buf, &acc);
printf("acc*b: %s\n\n", buf);
//new acc and b for divide test
build_dec80(&acc, "3.14", 88);
build_dec80(&b, "-1.5", -2);
dec80_to_str(buf, &acc);
printf(" acc: %s\n", buf);
dec80_to_str(buf, &b);
printf(" b: %s\n", buf);
div_decn(&acc, &b);
dec80_to_str(buf, &acc);
printf("acc/b: %s\n", buf);
return 0;
}