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Add the ieee754_mantissa() and ieee754_exponent() functions to the iee754

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extension.  Build the ieee754 extension into the CLI.

FossilOrigin-Name: db2f0836b64cd2e119684f1cf75fa3b19a84ca6aca1a239f7e2b9298016e2c95
This commit is contained in:
drh
2020-06-24 15:06:29 +00:00
parent ec18b6e5b9
commit 8cda77d44a
7 changed files with 104 additions and 31 deletions
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96
ext/misc/ieee754.c
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@ -26,10 +26,59 @@
**
** Examples:
**
** ieee754(2.0) -> 'ieee754(2,0)'
** ieee754(45.25) -> 'ieee754(181,-2)'
** ieee754(2, 0) -> 2.0
** ieee754(181, -2) -> 45.25
** ieee754(2.0) -> 'ieee754(2,0)'
** ieee754(45.25) -> 'ieee754(181,-2)'
** ieee754(2, 0) -> 2.0
** ieee754(181, -2) -> 45.25
**
** Two additional functions break apart the one-argument ieee754()
** result into separate integer values:
**
** ieee754_mantissa(45.25) -> 181
** ieee754_exponent(45.25) -> -2
**
** In all single-argument functions, if the argument is an 8-byte blob
** then that blob is interpreted as a big-endian binary64 value.
**
**
** EXACT DECIMAL REPRESENTATION OF BINARY64 VALUES
** -----------------------------------------------
**
** This extension in combination with the separate 'decimal' extension
** can be used to compute the exact decimal representation of binary64
** values. To begin, first compute a table of exponent values:
**
** CREATE TABLE pow2(x INTEGER PRIMARY KEY, v TEXT);
** WITH RECURSIVE c(x,v) AS (
** VALUES(0,'1')
** UNION ALL
** SELECT x+1, decimal_mul(v,'2') FROM c WHERE x+1<=971
** ) INSERT INTO pow2(x,v) SELECT x, v FROM c;
** WITH RECURSIVE c(x,v) AS (
** VALUES(-1,'0.5')
** UNION ALL
** SELECT x-1, decimal_mul(v,'0.5') FROM c WHERE x-1>=-1075
** ) INSERT INTO pow2(x,v) SELECT x, v FROM c;
**
** Then, to compute the exact decimal representation of a floating
** point value (the value 47.49 is used in the example) do:
**
** WITH c(n) AS (VALUES(47.49))
** ---------------^^^^^---- Replace with whatever you want
** SELECT decimal_mul(ieee754_mantissa(c.n),pow2.v)
** FROM pow2, c WHERE pow2.x=ieee754_exponent(c.n);
**
** Here is a query to show various boundry values for the binary64
** number format:
**
** WITH c(name,bin) AS (VALUES
** ('minimum positive value', x'0000000000000001'),
** ('maximum subnormal value', x'000fffffffffffff'),
** ('mininum positive nornal value', x'0010000000000000'),
** ('maximum value', x'7fefffffffffffff'))
** SELECT c.name, decimal_mul(ieee754_mantissa(c.bin),pow2.v)
** FROM pow2, c WHERE pow2.x=ieee754_exponent(c.bin);
**
*/
#include "sqlite3ext.h"
SQLITE_EXTENSION_INIT1
@ -88,10 +137,20 @@ static void ieee754func(
}
if( isNeg ) m = -m;
}
sqlite3_snprintf(sizeof(zResult), zResult, "ieee754(%lld,%d)",
m, e-1075);
sqlite3_result_text(context, zResult, -1, SQLITE_TRANSIENT);
}else if( argc==2 ){
switch( *(int*)sqlite3_user_data(context) ){
case 0:
sqlite3_snprintf(sizeof(zResult), zResult, "ieee754(%lld,%d)",
m, e-1075);
sqlite3_result_text(context, zResult, -1, SQLITE_TRANSIENT);
break;
case 1:
sqlite3_result_int64(context, m);
break;
case 2:
sqlite3_result_int(context, e-1075);
break;
}
}else{
sqlite3_int64 m, e, a;
double r;
int isNeg = 0;
@ -133,16 +192,25 @@ int sqlite3_ieee_init(
char **pzErrMsg,
const sqlite3_api_routines *pApi
){
static const struct {
char *zFName;
int nArg;
int iAux;
} aFunc[] = {
{ "ieee754", 1, 0 },
{ "ieee754", 2, 0 },
{ "ieee754_mantissa", 1, 1 },
{ "ieee754_exponent", 1, 2 },
};
int i;
int rc = SQLITE_OK;
SQLITE_EXTENSION_INIT2(pApi);
(void)pzErrMsg; /* Unused parameter */
rc = sqlite3_create_function(db, "ieee754", 1,
SQLITE_UTF8|SQLITE_INNOCUOUS, 0,
for(i=0; i<sizeof(aFunc)/sizeof(aFunc[0]) && rc==SQLITE_OK; i++){
rc = sqlite3_create_function(db, aFunc[i].zFName, aFunc[i].nArg,
SQLITE_UTF8|SQLITE_INNOCUOUS,
(void*)&aFunc[i].iAux,
ieee754func, 0, 0);
if( rc==SQLITE_OK ){
rc = sqlite3_create_function(db, "ieee754", 2,
SQLITE_UTF8|SQLITE_INNOCUOUS, 0,
ieee754func, 0, 0);
}
return rc;
}