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Final clean-up of the idea of using Dekker double-precision floating

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computations to improve accuracy.

FossilOrigin-Name: 40285d631072b79aba39cc20d4b217bdf0069f29ac9902cb97dec28d3e4cde11
This commit is contained in:
drh
2023-07-03 11:39:38 +00:00
parent bc2b65832e
commit 841e596ad0
3 changed files with 19 additions and 10 deletions
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15
src/util.c
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@@ -999,8 +999,8 @@ void sqlite3FpDecode(FpDecode *p, double r, int iRound, int mxRound){
/* Multiply r by powers of ten until it lands somewhere in between
** 1.0e+19 and 1.0e+17.
*/
if( sizeof(long double)>8 && 0 ){
long double rr = r;
if( sizeof(LONGDOUBLE_TYPE)>8 ){
LONGDOUBLE_TYPE rr = r;
if( rr>=1.0e+19 ){
while( rr>=1.0e+119L ){ exp+=100; rr *= 1.0e-100L; }
while( rr>=1.0e+29L ){ exp+=10; rr *= 1.0e-10L; }
@@ -1012,6 +1012,15 @@ void sqlite3FpDecode(FpDecode *p, double r, int iRound, int mxRound){
}
v = (u64)rr;
}else{
/* If high-precision floating point is not available using "long double",
** then use Dekker-style double-double computation to increase the
** precision.
**
** The error terms on constants like 1.0e+100 computed using the
** decimal extension, for example as follows:
**
** SELECT decimal_sci(decimal_sub('1.0e+100',decimal(1.0e+100)));
*/
double rr = 0.0;
if( r>1.84e+19 ){
while( r>1.84e+119 ){
@@ -1029,7 +1038,7 @@ void sqlite3FpDecode(FpDecode *p, double r, int iRound, int mxRound){
}else{
while( r<1.84e-82 ){
exp -= 100;
mul2(r, rr, 1.0e+100, -1.5902891109759918046, &r, &rr);
mul2(r, rr, 1.0e+100, -1.5902891109759918046e+83, &r, &rr);
}
while( r<1.84e+08 ){
exp -= 10;