7u83/stc_rpncalc
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bugfixes for addition/subtraction

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This commit is contained in:
Jeff Wang 2019-03-27 05:19:09 -04:00
parent a742bb2059
commit 0ba2ca7710
3 changed files with 30 additions and 27 deletions
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52
src/decn/decn.c
View File

@ -93,7 +93,7 @@ static void shift_left(dec80* x){
static void remove_leading_zeros(dec80* x){
uint8_t digit100;
uint8_t is_negative = (x->exponent < 0 ? 1 : 0);
uint8_t exponent = get_exponent(x);
int16_t exponent = get_exponent(x);
//find first non-zero digit100
for (digit100 = 0; digit100 < DEC80_NUM_LSU; digit100++){
@ -103,6 +103,7 @@ static void remove_leading_zeros(dec80* x){
}
exponent -= digit100 * 2; //base 100
//copy digit100s left if needed
if (digit100 != 0 && digit100 < DEC80_NUM_LSU){ //found non-zero digit100
uint8_t i;
//copy digit100s
@ -111,18 +112,15 @@ 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;
} else {
x->exponent = exponent & 0x7fff;
}
}
//ensure MSdigit in MSdigit100 is > 0
if (x->lsu[0] < 10) {
shift_left(x);
exponent--;
}
//write back exponent
set_exponent(x, exponent, is_negative);
}
void build_dec80(dec80* dest, const char* signif_str, int16_t exponent){
@ -448,11 +446,13 @@ static void sub_mag(dec80* acc, const dec80* x){
//normalize
remove_leading_zeros(acc);
remove_leading_zeros(&tmp);
_incr_exp(&tmp, get_exponent(acc));
if (get_exponent(acc) != get_exponent(&tmp)){
_incr_exp(&tmp, get_exponent(acc));
}
#ifdef DEBUG_ADD
extern char buf[DECN_BUF_SIZE];
dec80_to_str(buf, &tmp);
printf("incr_exp tmp: %s\n", buf);
printf(" incr_exp tmp: %s\n", buf);
#endif
//do subtraction
for (i = DEC80_NUM_LSU - 1; i >=0; i--){
@ -484,7 +484,7 @@ void add_decn(dec80* acc, const dec80* x){
return;
}
//handle cases where signs differ
if (acc->exponent < 0 && x->exponent > 0){
if (acc->exponent < 0 && x->exponent >= 0){
// -acc, +x
rel = compare_magn(acc, x);
if (rel == 1){
@ -508,7 +508,7 @@ void add_decn(dec80* acc, const dec80* x){
set_dec80_zero(acc);
return;
}
} else if (acc->exponent > 0 && x->exponent < 0){
} else if (acc->exponent >= 0 && x->exponent < 0){
// +acc, -x
rel = compare_magn(acc, x);
if (rel == 1){
@ -523,7 +523,6 @@ void add_decn(dec80* acc, const dec80* x){
#endif
copy_decn(&tmp, x);
sub_mag(&tmp, acc);
negate_decn(&tmp);
copy_decn(acc, &tmp);
return;
} else { //equal
@ -542,22 +541,25 @@ void add_decn(dec80* acc, const dec80* x){
#ifdef DEBUG_ADD
extern char buf[DECN_BUF_SIZE];
dec80_to_str(buf, acc);
printf("rem_leading_zeros acc: %s\n", buf);
printf(" rem_leading_zeros acc: %s\n", buf);
dec80_to_str(buf, &tmp);
printf("rem_leading_zeros tmp: %s\n", buf);
printf(" rem_leading_zeros tmp: %s\n", buf);
#endif
rel = compare_magn(acc, &tmp);
if (rel == 1){
if (get_exponent(acc) > get_exponent(&tmp)){
_incr_exp(&tmp, get_exponent(acc));
} else if (rel == -1){
_incr_exp(acc, get_exponent(&tmp));
} else if (get_exponent(acc) < get_exponent(&tmp)){
//shift significand and adjust exponent to match
for (i = 0; i < get_exponent(&tmp) - get_exponent(acc); i++){
shift_right(acc);
}
set_exponent(acc, get_exponent(&tmp), (acc->exponent < 0));
}
#ifdef DEBUG_ADD
extern char buf[DECN_BUF_SIZE];
dec80_to_str(buf, acc);
printf("incr_exp acc: %s\n", buf);
printf(" incr_exp acc: %s\n", buf);
dec80_to_str(buf, &tmp);
printf("incr_exp tmp: %s\n", buf);
printf(" incr_exp tmp: %s\n", buf);
#endif
//do addition
for (i = DEC80_NUM_LSU - 1; i >= 0; i--){

2
src/decn/decn.h
View File

@ -20,7 +20,7 @@
typedef struct {
int16_t exponent; //MSBit is sign of dec80 number, bottom 15 bits are 2's Compl exponent
uint8_t lsu[DEC80_NUM_LSU]; //lsu[0] holds most-significant 2 digits (base 100)
//implicit decimal point between (lsu[0]/100) and (lsu[0]%100)
//implicit decimal point between (lsu[0]/10) and (lsu[0]%10)
} dec80;
//remove sign bit, and return 15 bit exponent sign-extended to 16 bits

3
src/decn/decn_test.c
View File

@ -43,6 +43,7 @@ int main(void){
dec80_to_str(buf, &diff);
printf("\n : %s\n\n", buf);
//new acc for acc - b test
dec80_to_str(buf, &acc);
printf("acc: %s\n", buf);
negate_decn(&b);
@ -51,7 +52,7 @@ int main(void){
add_decn(&acc, &b);
dec80_to_str(buf, &acc);
//compare result
//compare result of new acc - b
printf("\nacc - b: %s", buf);
printf("\n : %s", "-9.234567890123456E3");
build_dec80(&diff, "-9.234567890123456", 3);