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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
__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];
@ -504,18 +507,16 @@ static void _incr_exp(dec80* acc, exp_t exponent){
}
//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
static void sub_mag(dec80* acc, const dec80* x){
static void sub_mag(){
int8_t i;
uint8_t carry = 0;
static __xdata dec80 tmp;
copy_decn(&tmp, x);
//normalize
remove_leading_zeros(acc);
remove_leading_zeros(&tmp);
if (get_exponent(acc) != get_exponent(&tmp)){
_incr_exp(&tmp, get_exponent(acc));
remove_leading_zeros(&AccDecn);
remove_leading_zeros(&BDecn);
if (get_exponent(&AccDecn) != get_exponent(&BDecn)){
_incr_exp(&BDecn, get_exponent(&AccDecn));
}
#ifdef DEBUG_ADD
decn_to_str_complete(&tmp);
@ -524,15 +525,15 @@ 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)){
digit100 = acc->lsu[i] - (tmp.lsu[i] + carry);
if (AccDecn.lsu[i] >= (BDecn.lsu[i] + carry)){
digit100 = AccDecn.lsu[i] - (BDecn.lsu[i] + carry);
carry = 0;
} else {
digit100 = acc->lsu[i] + 100 - (tmp.lsu[i] + carry);
digit100 = AccDecn.lsu[i] + 100 - (BDecn.lsu[i] + carry);
carry = 1;
}
assert(digit100 < 100);
acc->lsu[i] = digit100;
AccDecn.lsu[i] = digit100;
}
assert(carry == 0); //shouldn't be carry out if |acc| > |x|
}
@ -557,15 +558,16 @@ void add_decn(void){
#ifdef DEBUG_ADD
printf("|-acc| > |+x|\n");
#endif
sub_mag(&AccDecn, &BDecn);
sub_mag();
return;
} else if (rel == -1){
#ifdef DEBUG_ADD
printf("|-acc| < |+x|\n");
#endif
copy_decn(&TmpDecn, &BDecn);
sub_mag(&TmpDecn, &AccDecn);
copy_decn(&BDecn, &AccDecn);
copy_decn(&AccDecn, &TmpDecn);
sub_mag();
return;
} else { //equal
#ifdef DEBUG_ADD
@ -581,15 +583,16 @@ void add_decn(void){
#ifdef DEBUG_ADD
printf("|+acc| > |-x|\n");
#endif
sub_mag(&AccDecn, &BDecn);
sub_mag();
return;
} else if (rel == -1){
#ifdef DEBUG_ADD
printf("|+acc| < |-x|\n");
#endif
copy_decn(&TmpDecn, &BDecn);
sub_mag(&TmpDecn, &AccDecn);
copy_decn(&BDecn, &AccDecn);
copy_decn(&AccDecn, &TmpDecn);
sub_mag();
return;
} else { //equal
#ifdef DEBUG_ADD
@ -745,9 +748,9 @@ void mult_decn(void){
}
void div_decn(void){
static __xdata dec80 curr_recip; //copy of x, holds current 1/x estimate
static __xdata dec80 x_copy; //holds copy of original x
static __xdata dec80 acc_copy; //holds copy of original acc
#define CURR_RECIP Tmp2Decn //copy of x, holds current 1/x estimate
#define X_COPY Tmp3Decn //holds copy of original x
#define ACC_COPY Tmp4Decn //holds copy of original acc
uint8_t i;
exp_t initial_exp;
//check divide by zero
@ -764,9 +767,9 @@ void div_decn(void){
remove_leading_zeros(&AccDecn);
remove_leading_zeros(&BDecn);
//store copy of acc for final multiply by 1/x
copy_decn(&acc_copy, &AccDecn);
copy_decn(&ACC_COPY, &AccDecn);
//store copy of x
copy_decn(&x_copy, &BDecn);
copy_decn(&X_COPY, &BDecn);
//get initial exponent of estimate for 1/x
initial_exp = get_exponent(&BDecn);
#ifdef DEBUG_DIV
@ -777,28 +780,28 @@ void div_decn(void){
#ifdef DEBUG_DIV
printf(" -> %d\n", initial_exp);
#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
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){
curr_recip.lsu[0] = 30;
CURR_RECIP.lsu[0] = 30;
} else if (BDecn.lsu[0] < 50){
curr_recip.lsu[0] = 20;
CURR_RECIP.lsu[0] = 20;
} 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++){
curr_recip.lsu[i] = 0;
CURR_RECIP.lsu[i] = 0;
}
copy_decn(&AccDecn, &curr_recip);
copy_decn(&AccDecn, &CURR_RECIP);
//do newton raphson iterations
for (i = 0; i < 6; i++){ //just fix number of iterations for now
#ifdef DEBUG_DIV
decn_to_str_complete(&curr_recip);
printf("%2d: %s\n", i, Buf);
#endif
copy_decn(&BDecn, &x_copy);
copy_decn(&BDecn, &X_COPY);
mult_decn();
#ifdef DEBUG_DIV
decn_to_str_complete(&AccDecn);
@ -811,7 +814,7 @@ void div_decn(void){
decn_to_str_complete(&AccDecn);
printf(" %20s: %s\n", "(1-recip*x)", Buf);
#endif
copy_decn(&BDecn, &curr_recip);
copy_decn(&BDecn, &CURR_RECIP);
mult_decn();
#ifdef DEBUG_DIV
decn_to_str_complete(&AccDecn);
@ -819,11 +822,16 @@ void div_decn(void){
#endif
add_decn();
//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
copy_decn(&BDecn, &acc_copy);
copy_decn(&BDecn, &ACC_COPY);
mult_decn();
//try not to pollute namespace
#undef CURR_RECIP
#undef X_COPY
#undef ACC_COPY
}
static void set_str_error(){