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Literal string equality tests ... implement another optimisation, plus one

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spotted by Fred, plus a fix for another bug spotted by Fred!


git-svn-id: svn+ssh://svn.gna.org/svn/gnustep/libs/base/trunk@34102 72102866-910b-0410-8b05-ffd578937521
This commit is contained in:
rfm 2011-11-01 11:43:40 +00:00
parent 27807e706c
commit 0575536e78
1 changed files with 44 additions and 10 deletions
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54
Source/GSString.m
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@ -318,21 +318,26 @@ literalIsEqualInternal(NXConstantString *s, GSStr o)
if (0 == o->_flags.wide) if (0 == o->_flags.wide)
{ {
/* A narrow internal characterset must have ASCII as a subset, /* If the other string is a buffer containing ascii characters,
* and so does a UTF-8 string literal, so a bytewise comparison * we can perform a bytewise comparison.
* of strings that contain the same number of bytes will give
* a quick check for the common case where both are ASCII.
*/ */
if (len == s->nxcslen && 0 == memcmp(o->_contents.c, s->nxcsptr, len)) if (internalEncoding == NSASCIIStringEncoding)
{ {
return YES; if (len == s->nxcslen
&& 0 == memcmp(o->_contents.c, s->nxcsptr, len))
{
return YES;
}
else
{
return NO;
}
} }
/* If the other string is a buffer containing ascii or latin1, /* If the other string is a buffer containing latin1 characters,
* we can compare buffer contents with unichar values directly. * we can compare buffer contents with unichar values directly.
*/ */
if (internalEncoding == NSISOLatin1StringEncoding if (internalEncoding == NSISOLatin1StringEncoding)
|| internalEncoding == NSASCIIStringEncoding)
{ {
while (i < s->nxcslen || n > 0) while (i < s->nxcslen || n > 0)
{ {
@ -349,6 +354,35 @@ literalIsEqualInternal(NXConstantString *s, GSStr o)
} }
return YES; return YES;
} }
/* For any other narrow internal string, we know that ascii is
* a subset of the encoding, so as long as characters are ascii
* (don't have the top bit set) we can do bytewise comparison.
*/
if (len == s->nxcslen)
{
unsigned index;
for (index = 0; index < len; index++)
{
uint8_t c = s->nxcsptr[index];
if (c != o->_contents.c[index] || c >= 128)
{
/* Characters differ at this point.
*/
break;
}
}
if (index == len)
{
return YES;
}
/* The characters were the same up to 'index', so we won't
* need to recheck those first few characters.
*/
pos = i = index;
}
} }
/* For small strings, or ones where we already have an array of /* For small strings, or ones where we already have an array of
@ -356,7 +390,7 @@ literalIsEqualInternal(NXConstantString *s, GSStr o)
* For larger strings, we may do as well with a character by * For larger strings, we may do as well with a character by
* character comparison. * character comparison.
*/ */
if (1 == o->_flags.wide || len < 200) if (1 == o->_flags.wide || (len < 200 && pos < len))
{ {
unichar *ptr; unichar *ptr;