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Fast conversion of double when representable as long long

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This commit is contained in:
Pieter Noordhuis 2011-03-08 12:30:01 +01:00
parent 45290ad9bb
commit 672b0a1b25
2 changed files with 41 additions and 0 deletions
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1
src/redis.h
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@ -887,6 +887,7 @@ int stringmatchlen(const char *pattern, int patternLen,
int stringmatch(const char *pattern, const char *string, int nocase);
long long memtoll(const char *p, int *err);
int ll2string(char *s, size_t len, long long value);
int d2string(char *s, size_t len, double value);
int isStringRepresentableAsLong(sds s, long *longval);
int isStringRepresentableAsLongLong(sds s, long long *longval);
int isObjectRepresentableAsLongLong(robj *o, long long *llongval);

40
src/util.c
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@ -1,6 +1,7 @@
#include "redis.h"
#include <ctype.h>
#include <limits.h>
#include <math.h>
/* Glob-style pattern matching. */
int stringmatchlen(const char *pattern, int patternLen,
@ -200,6 +201,45 @@ int ll2string(char *s, size_t len, long long value) {
return l;
}
/* Convert a double to a string representation. Returns the number of bytes
* required. The representation should always be parsable by stdtod(3). */
int d2string(char *buf, size_t len, double value) {
if (isnan(value)) {
len = snprintf(buf,len,"nan");
} else if (isinf(value)) {
if (value < 0)
len = snprintf(buf,len,"-inf");
else
len = snprintf(buf,len,"inf");
} else if (value == 0) {
/* See: http://en.wikipedia.org/wiki/Signed_zero, "Comparisons". */
if (1.0/value < 0)
len = snprintf(buf,len,"-0");
else
len = snprintf(buf,len,"0");
} else {
#if (DBL_MANT_DIG >= 52) && (LLONG_MAX == 0x7fffffffffffffffLL)
/* Check if the float is in a safe range to be casted into a
* long long. We are assuming that long long is 64 bit here.
* Also we are assuming that there are no implementations around where
* double has precision < 52 bit.
*
* Under this assumptions we test if a double is inside an interval
* where casting to long long is safe. Then using two castings we
* make sure the decimal part is zero. If all this is true we use
* integer printing function that is much faster. */
double min = -4503599627370495; /* (2^52)-1 */
double max = 4503599627370496; /* -(2^52) */
if (val > min && val < max && value == ((double)((long long)value)))
len = ll2string(buf,len,(long long)value);
else
#endif
len = snprintf(buf,len,"%.17g",value);
}
return len;
}
/* Check if the sds string 's' can be represented by a long long
* (that is, is a number that fits into long without any other space or
* character before or after the digits, so that converting this number