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More intelligent exponentiation in strtod/strtol (#5487) - patch by Ben Millwood

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This commit is contained in:
Thilo Schulz 2012-07-01 16:43:28 +00:00
parent 8534c94e4c
commit ca44693f34
1 changed files with 44 additions and 64 deletions
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108
code/game/bg_lib.c
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@ -768,6 +768,43 @@ double atan2( double y, double x ) {
#endif #endif
/*
===============
powN
Raise a double to a integer power
===============
*/
static double powN( double base, int exp )
{
if( exp >= 0 )
{
double result = 1.0;
// calculate x, x^2, x^4, ... by repeated squaring
// and multiply together the ones corresponding to the
// binary digits of the exponent
// e.g. x^73 = x^(1 + 8 + 64) = x * x^8 * x^64
while( exp > 0 )
{
if( exp % 2 == 1 )
result *= base;
base *= base;
exp /= 2;
}
return result;
}
// if exp is INT_MIN, the next clause will be upset,
// because -exp isn't representable
else if( exp == INT_MIN )
return powN( base, exp + 1 ) / base;
// x < 0
else
return 1.0 / powN( base, -exp );
}
double tan( double x ) { double tan( double x ) {
return sin(x) / cos(x); return sin(x) / cos(x);
} }
@ -1042,7 +1079,6 @@ double strtod( const char *nptr, char **endptr )
if( end != s && tolower( *nptr ) == 'p' ) if( end != s && tolower( *nptr ) == 'p' )
{ {
int exp; int exp;
float res2;
// apparently (confusingly) the exponent should be // apparently (confusingly) the exponent should be
// decimal // decimal
exp = strtol( &nptr[1], (char **)&end, 10 ); exp = strtol( &nptr[1], (char **)&end, 10 );
@ -1053,28 +1089,8 @@ double strtod( const char *nptr, char **endptr )
*endptr = (char *)nptr; *endptr = (char *)nptr;
return res; return res;
} }
if( exp > 0 )
{ res *= powN( 2, exp );
while( exp-- > 0 )
{
res2 = res * 2;
// check for infinity
if( res2 <= res )
break;
res = res2;
}
}
else
{
while( exp++ < 0 )
{
res2 = res / 2;
// check for underflow
if( res2 >= res )
break;
res = res2;
}
}
} }
if( endptr ) if( endptr )
*endptr = (char *)end; *endptr = (char *)end;
@ -1108,7 +1124,6 @@ double strtod( const char *nptr, char **endptr )
if( p != end && tolower( *nptr ) == 'e' ) if( p != end && tolower( *nptr ) == 'e' )
{ {
int exp; int exp;
float res10;
exp = strtol( &nptr[1], (char **)&end, 10 ); exp = strtol( &nptr[1], (char **)&end, 10 );
if( &nptr[1] == end ) if( &nptr[1] == end )
{ {
@ -1117,30 +1132,8 @@ double strtod( const char *nptr, char **endptr )
*endptr = (char *)nptr; *endptr = (char *)nptr;
return res; return res;
} }
if( exp > 0 )
{ res *= powN( 10, exp );
while( exp-- > 0 )
{
res10 = res * 10;
// check for infinity to save us time
if( res10 <= res )
break;
res = res10;
}
}
else if( exp < 0 )
{
while( exp++ < 0 )
{
res10 = res / 10;
// check for underflow
// (test for 0 would probably be just
// as good)
if( res10 >= res )
break;
res = res10;
}
}
} }
if( endptr ) if( endptr )
*endptr = (char *)end; *endptr = (char *)end;
@ -1907,19 +1900,6 @@ static LDOUBLE abs_val (LDOUBLE value)
return result; return result;
} }
static LDOUBLE pow10 (int exp)
{
LDOUBLE result = 1;
while (exp)
{
result *= 10;
exp--;
}
return result;
}
static long round (LDOUBLE value) static long round (LDOUBLE value)
{ {
long intpart; long intpart;
@ -1982,12 +1962,12 @@ static int fmtfp (char *buffer, size_t *currlen, size_t maxlen,
/* We "cheat" by converting the fractional part to integer by /* We "cheat" by converting the fractional part to integer by
* multiplying by a factor of 10 * multiplying by a factor of 10
*/ */
fracpart = round ((pow10 (max)) * (ufvalue - intpart)); fracpart = round ((powN (10, max)) * (ufvalue - intpart));
if (fracpart >= pow10 (max)) if (fracpart >= powN (10, max))
{ {
intpart++; intpart++;
fracpart -= pow10 (max); fracpart -= powN (10, max);
} }
#ifdef DEBUG_SNPRINTF #ifdef DEBUG_SNPRINTF