7u83/stc_rpncalc
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bugfixes for addition/subtraction

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This commit is contained in:
Jeff Wang 2019-03-26 04:45:09 -04:00
parent 72becb60a7
commit d2faa41dd5
1 changed files with 87 additions and 39 deletions
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126
src/decn/decn.c
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@ -7,12 +7,14 @@
#include "../utils.h"
#define DEBUG
#define DEBUG_ADD
//#define DEBUG
//#define DEBUG_ADD
//#define DEBUG_COMPARE_MAGN
#ifndef DESKTOP
#undef DEBUG
#undef DEBUG_ADD
#undef DEBUG_COMPARE_MAGN
#endif
#ifdef DESKTOP
@ -42,9 +44,9 @@ void copy_decn(dec80* dest, const dec80* src){
int16_t get_exponent(const dec80* x){
int16_t exponent = x->exponent;
if (exponent & 0x4000){ //negative
return (uint16_t) exponent | 0x8000;
return exponent | 0x8000;
} else { //positive
return (uint16_t) exponent & 0x7fff;
return exponent & 0x7fff;
}
}
@ -55,6 +57,28 @@ static void zero_remaining_dec80(dec80* dest, uint8_t digit100){
}
}
static void shift_right(dec80* x){
uint8_t high = 0, low = 0, old_low = 0;
uint8_t i;
for (i = 0; i < DEC80_NUM_LSU; i++){
high = x->lsu[i] / 10;
low = x->lsu[i] % 10;
x->lsu[i] = high + (old_low*10);
old_low = low;
}
}
static void shift_left(dec80* x){
uint8_t high = 0, low = 0, old_high = 0;
int8_t i;
for (i = DEC80_NUM_LSU - 1; i >= 0 ; i--){
high = x->lsu[i] / 10;
low = x->lsu[i] % 10;
x->lsu[i] = old_high + (low*10);
old_high = high;
}
}
static void remove_leading_zeros(dec80* x){
uint8_t digit100;
uint8_t is_negative = (x->exponent < 0 ? 1 : 0);
@ -76,6 +100,11 @@ static void remove_leading_zeros(dec80* x){
}
//zero out remaining digit100s, now that number left-aligned
zero_remaining_dec80(x, i);
//ensure MSdigit in MSdigit100 is > 0
if (x->lsu[digit100] < 10) {
shift_left(x);
exponent--;
}
//write back exponent
if (is_negative){
x->exponent = exponent | 0x8000;
@ -85,17 +114,6 @@ static void remove_leading_zeros(dec80* x){
}
}
static void shift_right(dec80* x){
uint8_t high = 0, low = 0, old_low = 0;
uint8_t i;
for (i = 0; i < DEC80_NUM_LSU; i++){
high = x->lsu[i] / 10;
low = x->lsu[i] % 10;
x->lsu[i] = high + (old_low*10);
old_low = low;
}
}
void build_dec80(dec80* dest, const char* signif_str, int16_t exponent){
enum {
SIGN_ZERO,
@ -302,7 +320,7 @@ void set_dec80_NaN(dec80* dest){
}
void negate_decn(dec80* x){
static const int16_t xor_val = 0x8000;
static const int16_t xor_val = -(0x7fff) - 1;
(x->exponent) ^= xor_val;
}
@ -310,42 +328,54 @@ int8_t compare_magn(const dec80* a, const dec80* b){ //a<b: -1, a==b: 0, a>b: 1
uint8_t a_i, b_i;
int16_t a_exp=0, b_exp=0;
int8_t a_signif_b = 0; //a<b: -1, a==b: 0, a>b: 1
//discard leading zeros
for (a_i = 0; a_i < DEC80_NUM_LSU; a_i++){
if (a->lsu[a_i] != 0){
if (a->lsu[a_i] > 10){
a_exp++;
}
break;
}
}
for (b_i = 0; b_i < DEC80_NUM_LSU; b_i++){
if (b->lsu[b_i] != 0){
if (b->lsu[b_i] > 10){
b_exp++;
}
break;
}
}
dec80 a_tmp, b_tmp;
//copy
copy_decn(&a_tmp, a);
copy_decn(&b_tmp, b);
//normalize
remove_leading_zeros(&a_tmp);
remove_leading_zeros(&b_tmp);
//compare signifcands while tracking magnitude
for ( ; a_i < DEC80_NUM_LSU && b_i < DEC80_NUM_LSU; a_i++, b_i++, a_exp+=2, b_exp+=2){
for (
a_i = 0, b_i = 0;
a_i < DEC80_NUM_LSU && b_i < DEC80_NUM_LSU;
a_i++, b_i++, a_exp+=2, b_exp+=2
)
{
//set signif. inequality if this is first digit that is different
if (a_signif_b == 0 && (a->lsu[a_i] < b->lsu[b_i])){
if (a_signif_b == 0 && (a_tmp.lsu[a_i] < b_tmp.lsu[b_i])){
#ifdef DEBUG_COMPARE_MAGN
printf("a_signif_b -1: a.lsu[%d]=%d, b.lsu[%d]=%d\n",
a_i, a_tmp.lsu[a_i], b_i, b_tmp.lsu[b_i]);
#endif
a_signif_b = -1;
} else if (a_signif_b == 0 && (a->lsu[a_i] > b->lsu[b_i])){
} else if (a_signif_b == 0 && (a_tmp.lsu[a_i] > b_tmp.lsu[b_i])){
#ifdef DEBUG_COMPARE_MAGN
printf("a_signif_b 1: a.lsu[%d]=%d, b.lsu[%d]=%d\n",
a_i, a_tmp.lsu[a_i], b_i, b_tmp.lsu[b_i]);
#endif
a_signif_b = 1;
}
}
//calculate exponents
a_exp += get_exponent(a);
b_exp += get_exponent(b);
a_exp += get_exponent(&a_tmp);
b_exp += get_exponent(&b_tmp);
//compare exponents
if (a_exp > b_exp){
#ifdef DEBUG
printf("a_exp > b_exp\n");
#endif
return 1;
} else if (a_exp < b_exp){
#ifdef DEBUG
printf("a_exp < b_exp\n");
#endif
return -1;
}
//exponents equal, compare by significand
#ifdef DEBUG
printf("a_signif_b (%d)\n", a_signif_b);
#endif
return a_signif_b;
}
@ -421,7 +451,7 @@ static void sub_mag(dec80* acc, const dec80* x){
//do subtraction
for (i = DEC80_NUM_LSU - 1; i >=0; i--){
uint8_t digit100;
if (acc->lsu[i] > (tmp.lsu[i] + carry)){
if (acc->lsu[i] >= (tmp.lsu[i] + carry)){
digit100 = acc->lsu[i] - (tmp.lsu[i] + carry);
carry = 0;
} else {
@ -452,14 +482,23 @@ void add_decn(dec80* acc, const dec80* x){
// -acc, +x
rel = compare_magn(acc, x);
if (rel == 1){
#ifdef DEBUG_ADD
printf("|-acc| > |+x|\n");
#endif
sub_mag(acc, x);
return;
} else if (rel == -1){
#ifdef DEBUG_ADD
printf("|-acc| < |+x|\n");
#endif
copy_decn(&tmp, x);
sub_mag(&tmp, acc);
copy_decn(acc, &tmp);
return;
} else { //equal
#ifdef DEBUG_ADD
printf("|-acc| == |+x|\n");
#endif
set_dec80_zero(acc);
return;
}
@ -467,15 +506,24 @@ void add_decn(dec80* acc, const dec80* x){
// +acc, -x
rel = compare_magn(acc, x);
if (rel == 1){
#ifdef DEBUG_ADD
printf("|+acc| > |-x|\n");
#endif
sub_mag(acc, x);
return;
} else if (rel == -1){
#ifdef DEBUG_ADD
printf("|+acc| < |-x|\n");
#endif
copy_decn(&tmp, x);
sub_mag(&tmp, acc);
negate_decn(&tmp);
copy_decn(acc, &tmp);
return;
} else { //equal
#ifdef DEBUG_ADD
printf("|+acc| == |-x|\n");
#endif
set_dec80_zero(acc);
return;
}