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Smaller and faster sqlite3IsNaN() implementation makes deserialization of

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floating point values much faster.

FossilOrigin-Name: ea748edecb261f2b862d542daff6e99a6fd8879a8ace94b440d99e110577d1c1
This commit is contained in:
drh
2019-05-30 00:46:37 +00:00
parent 8a3884efae
commit 05921223c2
5 changed files with 18 additions and 50 deletions
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4
src/sqliteInt.h
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@@ -3802,8 +3802,12 @@ void sqlite3MutexWarnOnContention(sqlite3_mutex*);
#endif
#ifndef SQLITE_OMIT_FLOATING_POINT
# define EXP754 (((u64)0x7ff)<<52)
# define MAN754 ((((u64)1)<<52)-1)
# define IsNaN(X) (((X)&EXP754)==EXP754 && ((X)&MAN754)!=0)
int sqlite3IsNaN(double);
#else
# define IsNaN(X) 0
# define sqlite3IsNaN(X) 0
#endif

42
src/util.c
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@@ -58,47 +58,11 @@ int sqlite3FaultSim(int iTest){
#ifndef SQLITE_OMIT_FLOATING_POINT
/*
** Return true if the floating point value is Not a Number (NaN).
**
** Use the math library isnan() function if compiled with SQLITE_HAVE_ISNAN.
** Otherwise, we have our own implementation that works on most systems.
*/
int sqlite3IsNaN(double x){
int rc; /* The value return */
#if !SQLITE_HAVE_ISNAN && !HAVE_ISNAN
/*
** Systems that support the isnan() library function should probably
** make use of it by compiling with -DSQLITE_HAVE_ISNAN. But we have
** found that many systems do not have a working isnan() function so
** this implementation is provided as an alternative.
**
** This NaN test sometimes fails if compiled on GCC with -ffast-math.
** On the other hand, the use of -ffast-math comes with the following
** warning:
**
** This option [-ffast-math] should never be turned on by any
** -O option since it can result in incorrect output for programs
** which depend on an exact implementation of IEEE or ISO
** rules/specifications for math functions.
**
** Under MSVC, this NaN test may fail if compiled with a floating-
** point precision mode other than /fp:precise. From the MSDN
** documentation:
**
** The compiler [with /fp:precise] will properly handle comparisons
** involving NaN. For example, x != x evaluates to true if x is NaN
** ...
*/
#ifdef __FAST_MATH__
# error SQLite will not work correctly with the -ffast-math option of GCC.
#endif
volatile double y = x;
volatile double z = y;
rc = (y!=z);
#else /* if HAVE_ISNAN */
rc = isnan(x);
#endif /* HAVE_ISNAN */
testcase( rc );
return rc;
u64 y;
memcpy(&y,&x,sizeof(y));
return IsNaN(y);
}
#endif /* SQLITE_OMIT_FLOATING_POINT */

4
src/vdbeaux.c
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@@ -3652,7 +3652,7 @@ u32 sqlite3VdbeSerialPut(u8 *buf, Mem *pMem, u32 serial_type){
** routine so that in most cases the overhead of moving the stack pointer
** is avoided.
*/
static u32 SQLITE_NOINLINE serialGet(
static u32 serialGet(
const unsigned char *buf, /* Buffer to deserialize from */
u32 serial_type, /* Serial type to deserialize */
Mem *pMem /* Memory cell to write value into */
@@ -3684,7 +3684,7 @@ static u32 SQLITE_NOINLINE serialGet(
assert( sizeof(x)==8 && sizeof(pMem->u.r)==8 );
swapMixedEndianFloat(x);
memcpy(&pMem->u.r, &x, sizeof(x));
pMem->flags = sqlite3IsNaN(pMem->u.r) ? MEM_Null : MEM_Real;
pMem->flags = IsNaN(x) ? MEM_Null : MEM_Real;
}
return 8;
}