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use global registers for division, have sub_mag() operate directly on Accum and B

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This commit is contained in:
Jeff Wang 2019-09-23 23:46:58 -04:00
parent 747355222d
commit 4f020da222
1 changed files with 41 additions and 33 deletions
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74
src/decn/decn.c
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@ -44,7 +44,10 @@ static const uint8_t num_digits_display = 16;
#endif #endif
__idata dec80 AccDecn, BDecn; __idata dec80 AccDecn, BDecn;
__idata dec80 TmpDecn; __idata dec80 TmpDecn; //used by add_decn() and mult_decn()
__idata dec80 Tmp2Decn; //used by div_decn()
__idata dec80 Tmp3Decn; //used by div_decn()
__idata dec80 Tmp4Decn; //used by div_decn()
__xdata char Buf[DECN_BUF_SIZE]; __xdata char Buf[DECN_BUF_SIZE];
@ -504,18 +507,16 @@ static void _incr_exp(dec80* acc, exp_t exponent){
} }
//for internal use only, //for internal use only,
//acc must be larger than x in absolute value //AccDecn must be larger than BDecn in absolute value
//subtract by equal addition algorithm //subtract by equal addition algorithm
static void sub_mag(dec80* acc, const dec80* x){ static void sub_mag(){
int8_t i; int8_t i;
uint8_t carry = 0; uint8_t carry = 0;
static __xdata dec80 tmp;
copy_decn(&tmp, x);
//normalize //normalize
remove_leading_zeros(acc); remove_leading_zeros(&AccDecn);
remove_leading_zeros(&tmp); remove_leading_zeros(&BDecn);
if (get_exponent(acc) != get_exponent(&tmp)){ if (get_exponent(&AccDecn) != get_exponent(&BDecn)){
_incr_exp(&tmp, get_exponent(acc)); _incr_exp(&BDecn, get_exponent(&AccDecn));
} }
#ifdef DEBUG_ADD #ifdef DEBUG_ADD
decn_to_str_complete(&tmp); decn_to_str_complete(&tmp);
@ -524,15 +525,15 @@ static void sub_mag(dec80* acc, const dec80* x){
//do subtraction //do subtraction
for (i = DEC80_NUM_LSU - 1; i >=0; i--){ for (i = DEC80_NUM_LSU - 1; i >=0; i--){
uint8_t digit100; uint8_t digit100;
if (acc->lsu[i] >= (tmp.lsu[i] + carry)){ if (AccDecn.lsu[i] >= (BDecn.lsu[i] + carry)){
digit100 = acc->lsu[i] - (tmp.lsu[i] + carry); digit100 = AccDecn.lsu[i] - (BDecn.lsu[i] + carry);
carry = 0; carry = 0;
} else { } else {
digit100 = acc->lsu[i] + 100 - (tmp.lsu[i] + carry); digit100 = AccDecn.lsu[i] + 100 - (BDecn.lsu[i] + carry);
carry = 1; carry = 1;
} }
assert(digit100 < 100); assert(digit100 < 100);
acc->lsu[i] = digit100; AccDecn.lsu[i] = digit100;
} }
assert(carry == 0); //shouldn't be carry out if |acc| > |x| assert(carry == 0); //shouldn't be carry out if |acc| > |x|
} }
@ -557,15 +558,16 @@ void add_decn(void){
#ifdef DEBUG_ADD #ifdef DEBUG_ADD
printf("|-acc| > |+x|\n"); printf("|-acc| > |+x|\n");
#endif #endif
sub_mag(&AccDecn, &BDecn); sub_mag();
return; return;
} else if (rel == -1){ } else if (rel == -1){
#ifdef DEBUG_ADD #ifdef DEBUG_ADD
printf("|-acc| < |+x|\n"); printf("|-acc| < |+x|\n");
#endif #endif
copy_decn(&TmpDecn, &BDecn); copy_decn(&TmpDecn, &BDecn);
sub_mag(&TmpDecn, &AccDecn); copy_decn(&BDecn, &AccDecn);
copy_decn(&AccDecn, &TmpDecn); copy_decn(&AccDecn, &TmpDecn);
sub_mag();
return; return;
} else { //equal } else { //equal
#ifdef DEBUG_ADD #ifdef DEBUG_ADD
@ -581,15 +583,16 @@ void add_decn(void){
#ifdef DEBUG_ADD #ifdef DEBUG_ADD
printf("|+acc| > |-x|\n"); printf("|+acc| > |-x|\n");
#endif #endif
sub_mag(&AccDecn, &BDecn); sub_mag();
return; return;
} else if (rel == -1){ } else if (rel == -1){
#ifdef DEBUG_ADD #ifdef DEBUG_ADD
printf("|+acc| < |-x|\n"); printf("|+acc| < |-x|\n");
#endif #endif
copy_decn(&TmpDecn, &BDecn); copy_decn(&TmpDecn, &BDecn);
sub_mag(&TmpDecn, &AccDecn); copy_decn(&BDecn, &AccDecn);
copy_decn(&AccDecn, &TmpDecn); copy_decn(&AccDecn, &TmpDecn);
sub_mag();
return; return;
} else { //equal } else { //equal
#ifdef DEBUG_ADD #ifdef DEBUG_ADD
@ -745,9 +748,9 @@ void mult_decn(void){
} }
void div_decn(void){ void div_decn(void){
static __xdata dec80 curr_recip; //copy of x, holds current 1/x estimate #define CURR_RECIP Tmp2Decn //copy of x, holds current 1/x estimate
static __xdata dec80 x_copy; //holds copy of original x #define X_COPY Tmp3Decn //holds copy of original x
static __xdata dec80 acc_copy; //holds copy of original acc #define ACC_COPY Tmp4Decn //holds copy of original acc
uint8_t i; uint8_t i;
exp_t initial_exp; exp_t initial_exp;
//check divide by zero //check divide by zero
@ -764,9 +767,9 @@ void div_decn(void){
remove_leading_zeros(&AccDecn); remove_leading_zeros(&AccDecn);
remove_leading_zeros(&BDecn); remove_leading_zeros(&BDecn);
//store copy of acc for final multiply by 1/x //store copy of acc for final multiply by 1/x
copy_decn(&acc_copy, &AccDecn); copy_decn(&ACC_COPY, &AccDecn);
//store copy of x //store copy of x
copy_decn(&x_copy, &BDecn); copy_decn(&X_COPY, &BDecn);
//get initial exponent of estimate for 1/x //get initial exponent of estimate for 1/x
initial_exp = get_exponent(&BDecn); initial_exp = get_exponent(&BDecn);
#ifdef DEBUG_DIV #ifdef DEBUG_DIV
@ -777,28 +780,28 @@ void div_decn(void){
#ifdef DEBUG_DIV #ifdef DEBUG_DIV
printf(" -> %d\n", initial_exp); printf(" -> %d\n", initial_exp);
#endif #endif
set_exponent(&curr_recip, initial_exp, (BDecn.exponent < 0)); //set exponent, copy sign set_exponent(&CURR_RECIP, initial_exp, (BDecn.exponent < 0)); //set exponent, copy sign
//get initial estimate for 1/x //get initial estimate for 1/x
if (BDecn.lsu[0] < 20){ //mantissa between 1 and 2 if (BDecn.lsu[0] < 20){ //mantissa between 1 and 2
curr_recip.lsu[0] = 50; //0.50 with implicit point and exponent CURR_RECIP.lsu[0] = 50; //0.50 with implicit point and exponent
} else if (BDecn.lsu[0] < 33){ } else if (BDecn.lsu[0] < 33){
curr_recip.lsu[0] = 30; CURR_RECIP.lsu[0] = 30;
} else if (BDecn.lsu[0] < 50){ } else if (BDecn.lsu[0] < 50){
curr_recip.lsu[0] = 20; CURR_RECIP.lsu[0] = 20;
} else { } else {
curr_recip.lsu[0] = 10; //0.1 with implicit point and exponent CURR_RECIP.lsu[0] = 10; //0.1 with implicit point and exponent
} }
for (i = 1; i < DEC80_NUM_LSU; i++){ for (i = 1; i < DEC80_NUM_LSU; i++){
curr_recip.lsu[i] = 0; CURR_RECIP.lsu[i] = 0;
} }
copy_decn(&AccDecn, &curr_recip); copy_decn(&AccDecn, &CURR_RECIP);
//do newton raphson iterations //do newton raphson iterations
for (i = 0; i < 6; i++){ //just fix number of iterations for now for (i = 0; i < 6; i++){ //just fix number of iterations for now
#ifdef DEBUG_DIV #ifdef DEBUG_DIV
decn_to_str_complete(&curr_recip); decn_to_str_complete(&curr_recip);
printf("%2d: %s\n", i, Buf); printf("%2d: %s\n", i, Buf);
#endif #endif
copy_decn(&BDecn, &x_copy); copy_decn(&BDecn, &X_COPY);
mult_decn(); mult_decn();
#ifdef DEBUG_DIV #ifdef DEBUG_DIV
decn_to_str_complete(&AccDecn); decn_to_str_complete(&AccDecn);
@ -811,7 +814,7 @@ void div_decn(void){
decn_to_str_complete(&AccDecn); decn_to_str_complete(&AccDecn);
printf(" %20s: %s\n", "(1-recip*x)", Buf); printf(" %20s: %s\n", "(1-recip*x)", Buf);
#endif #endif
copy_decn(&BDecn, &curr_recip); copy_decn(&BDecn, &CURR_RECIP);
mult_decn(); mult_decn();
#ifdef DEBUG_DIV #ifdef DEBUG_DIV
decn_to_str_complete(&AccDecn); decn_to_str_complete(&AccDecn);
@ -819,11 +822,16 @@ void div_decn(void){
#endif #endif
add_decn(); add_decn();
//new_est(acc) = recip + (1 - recip*x)*recip, where tmp is current recip estimate //new_est(acc) = recip + (1 - recip*x)*recip, where tmp is current recip estimate
copy_decn(&curr_recip, &AccDecn); copy_decn(&CURR_RECIP, &AccDecn);
} }
//acc now holds 1/x, multiply by original acc to complete division //acc now holds 1/x, multiply by original acc to complete division
copy_decn(&BDecn, &acc_copy); copy_decn(&BDecn, &ACC_COPY);
mult_decn(); mult_decn();
//try not to pollute namespace
#undef CURR_RECIP
#undef X_COPY
#undef ACC_COPY
} }
static void set_str_error(){ static void set_str_error(){