pgstrcasecmp.c

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/*-------------------------------------------------------------------------
 *
 * pgstrcasecmp.c
 *     Portable SQL-like case-independent comparisons and conversions.
 *
 * SQL99 specifies Unicode-aware case normalization, which we don't yet
 * have the infrastructure for.  Instead we use tolower() to provide a
 * locale-aware translation.  However, there are some locales where this
 * is not right either (eg, Turkish may do strange things with 'i' and
 * 'I').  Our current compromise is to use tolower() for characters with
 * the high bit set, and use an ASCII-only downcasing for 7-bit
 * characters.
 *
 * NB: this code should match downcase_truncate_identifier() in scansup.c.
 *
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 *
 * src/port/pgstrcasecmp.c
 *
 *-------------------------------------------------------------------------
 */
#include "c.h"
 
#include <ctype.h>
 
 
/*
 * Case-independent comparison of two null-terminated strings.
 */
int
pg_strcasecmp(const char *s1, const char *s2)
{
    for (;;)
    {
        unsigned char ch1 = (unsigned char) *s1++;
        unsigned char ch2 = (unsigned char) *s2++;
 
        if (ch1 != ch2)
        {
            if (ch1 >= 'A' && ch1 <= 'Z')
                ch1 += 'a' - 'A';
            else if (IS_HIGHBIT_SET(ch1) && isupper(ch1))
                ch1 = tolower(ch1);
 
            if (ch2 >= 'A' && ch2 <= 'Z')
                ch2 += 'a' - 'A';
            else if (IS_HIGHBIT_SET(ch2) && isupper(ch2))
                ch2 = tolower(ch2);
 
            if (ch1 != ch2)
                return (int) ch1 - (int) ch2;
        }
        if (ch1 == 0)
            break;
    }
    return 0;
}
 
/*
 * Case-independent comparison of two not-necessarily-null-terminated strings.
 * At most n bytes will be examined from each string.
 */
int
pg_strncasecmp(const char *s1, const char *s2, size_t n)
{
    while (n-- > 0)
    {
        unsigned char ch1 = (unsigned char) *s1++;
        unsigned char ch2 = (unsigned char) *s2++;
 
        if (ch1 != ch2)
        {
            if (ch1 >= 'A' && ch1 <= 'Z')
                ch1 += 'a' - 'A';
            else if (IS_HIGHBIT_SET(ch1) && isupper(ch1))
                ch1 = tolower(ch1);
 
            if (ch2 >= 'A' && ch2 <= 'Z')
                ch2 += 'a' - 'A';
            else if (IS_HIGHBIT_SET(ch2) && isupper(ch2))
                ch2 = tolower(ch2);
 
            if (ch1 != ch2)
                return (int) ch1 - (int) ch2;
        }
        if (ch1 == 0)
            break;
    }
    return 0;
}
 
/*
 * Fold a character to upper case.
 *
 * Unlike some versions of toupper(), this is safe to apply to characters
 * that aren't lower case letters.  Note however that the whole thing is
 * a bit bogus for multibyte character sets.
 */
unsigned char
pg_toupper(unsigned char ch)
{
    if (ch >= 'a' && ch <= 'z')
        ch += 'A' - 'a';
    else if (IS_HIGHBIT_SET(ch) && islower(ch))
        ch = toupper(ch);
    return ch;
}
 
/*
 * Fold a character to lower case.
 *
 * Unlike some versions of tolower(), this is safe to apply to characters
 * that aren't upper case letters.  Note however that the whole thing is
 * a bit bogus for multibyte character sets.
 */
unsigned char
pg_tolower(unsigned char ch)
{
    if (ch >= 'A' && ch <= 'Z')
        ch += 'a' - 'A';
    else if (IS_HIGHBIT_SET(ch) && isupper(ch))
        ch = tolower(ch);
    return ch;
}