Allow pg_locale_t APIs to work when ctype_is_c.

Previously, the caller needed to check ctype_is_c first for some
routines and not others. Now, the APIs consistently work, and the
caller can just check ctype_is_c for optimization purposes.

Discussion: https://postgr.es/m/450ceb6260cad30d7afdf155d991a9caafee7c0d.camel@j-davis.com
Reviewed-by: Chao Li <li.evan.chao@gmail.com>

src/backend/utils/adt/pg_locale.c

@@ -1257,35 +1257,99 @@ get_collation_actual_version(char collprovider, const char *collcollate)
 	return collversion;
 }
 
+/* lowercasing/casefolding in C locale */
+static size_t
+strlower_c(char *dst, size_t dstsize, const char *src, ssize_t srclen)
+{
+	int			i;
+
+	srclen = (srclen >= 0) ? srclen : strlen(src);
+	for (i = 0; i < srclen && i < dstsize; i++)
+		dst[i] = pg_ascii_tolower(src[i]);
+	if (i < dstsize)
+		dst[i] = '\0';
+	return srclen;
+}
+
+/* titlecasing in C locale */
+static size_t
+strtitle_c(char *dst, size_t dstsize, const char *src, ssize_t srclen)
+{
+	bool		wasalnum = false;
+	int			i;
+
+	srclen = (srclen >= 0) ? srclen : strlen(src);
+	for (i = 0; i < srclen && i < dstsize; i++)
+	{
+		char		c = src[i];
+
+		if (wasalnum)
+			dst[i] = pg_ascii_tolower(c);
+		else
+			dst[i] = pg_ascii_toupper(c);
+
+		wasalnum = ((c >= '0' && c <= '9') ||
+					(c >= 'A' && c <= 'Z') ||
+					(c >= 'a' && c <= 'z'));
+	}
+	if (i < dstsize)
+		dst[i] = '\0';
+	return srclen;
+}
+
+/* uppercasing in C locale */
+static size_t
+strupper_c(char *dst, size_t dstsize, const char *src, ssize_t srclen)
+{
+	int			i;
+
+	srclen = (srclen >= 0) ? srclen : strlen(src);
+	for (i = 0; i < srclen && i < dstsize; i++)
+		dst[i] = pg_ascii_toupper(src[i]);
+	if (i < dstsize)
+		dst[i] = '\0';
+	return srclen;
+}
+
 size_t
 pg_strlower(char *dst, size_t dstsize, const char *src, ssize_t srclen,
 			pg_locale_t locale)
 {
-	return locale->ctype->strlower(dst, dstsize, src, srclen, locale);
+	if (locale->ctype == NULL)
+		return strlower_c(dst, dstsize, src, srclen);
+	else
+		return locale->ctype->strlower(dst, dstsize, src, srclen, locale);
 }
 
 size_t
 pg_strtitle(char *dst, size_t dstsize, const char *src, ssize_t srclen,
 			pg_locale_t locale)
 {
-	return locale->ctype->strtitle(dst, dstsize, src, srclen, locale);
+	if (locale->ctype == NULL)
+		return strtitle_c(dst, dstsize, src, srclen);
+	else
+		return locale->ctype->strtitle(dst, dstsize, src, srclen, locale);
 }
 
 size_t
 pg_strupper(char *dst, size_t dstsize, const char *src, ssize_t srclen,
 			pg_locale_t locale)
 {
-	return locale->ctype->strupper(dst, dstsize, src, srclen, locale);
+	if (locale->ctype == NULL)
+		return strupper_c(dst, dstsize, src, srclen);
+	else
+		return locale->ctype->strupper(dst, dstsize, src, srclen, locale);
 }
 
 size_t
 pg_strfold(char *dst, size_t dstsize, const char *src, ssize_t srclen,
 		   pg_locale_t locale)
 {
-	if (locale->ctype->strfold)
-		return locale->ctype->strfold(dst, dstsize, src, srclen, locale);
+	/* in the C locale, casefolding is the same as lowercasing */
+	if (locale->ctype == NULL)
+		return strlower_c(dst, dstsize, src, srclen);
 	else
-		return locale->ctype->strlower(dst, dstsize, src, srclen, locale);
+		return locale->ctype->strfold(dst, dstsize, src, srclen, locale);
 }
 
 /*
@@ -1560,6 +1624,8 @@ pg_towlower(pg_wchar wc, pg_locale_t locale)
 bool
 char_is_cased(char ch, pg_locale_t locale)
 {
+	if (locale->ctype == NULL)
+		return (ch >= 'A' && ch <= 'Z') || (ch >= 'a' && ch <= 'z');
 	return locale->ctype->char_is_cased(ch, locale);
 }
 
@@ -1571,6 +1637,8 @@ char_is_cased(char ch, pg_locale_t locale)
 bool
 char_tolower_enabled(pg_locale_t locale)
 {
+	if (locale->ctype == NULL)
+		return true;
 	return (locale->ctype->char_tolower != NULL);
 }
 
@@ -1582,6 +1650,8 @@ char_tolower_enabled(pg_locale_t locale)
 char
 char_tolower(unsigned char ch, pg_locale_t locale)
 {
+	if (locale->ctype == NULL)
+		return pg_ascii_tolower(ch);
 	return locale->ctype->char_tolower(ch, locale);
 }
 

src/backend/utils/adt/pg_locale_libc.c

@@ -326,6 +326,8 @@ static const struct ctype_methods ctype_methods_libc_sb = {
 	.strlower = strlower_libc_sb,
 	.strtitle = strtitle_libc_sb,
 	.strupper = strupper_libc_sb,
+	/* in libc, casefolding is the same as lowercasing */
+	.strfold = strlower_libc_sb,
 	.wc_isdigit = wc_isdigit_libc_sb,
 	.wc_isalpha = wc_isalpha_libc_sb,
 	.wc_isalnum = wc_isalnum_libc_sb,
@@ -351,6 +353,8 @@ static const struct ctype_methods ctype_methods_libc_other_mb = {
 	.strlower = strlower_libc_mb,
 	.strtitle = strtitle_libc_mb,
 	.strupper = strupper_libc_mb,
+	/* in libc, casefolding is the same as lowercasing */
+	.strfold = strlower_libc_mb,
 	.wc_isdigit = wc_isdigit_libc_sb,
 	.wc_isalpha = wc_isalpha_libc_sb,
 	.wc_isalnum = wc_isalnum_libc_sb,
@@ -372,6 +376,8 @@ static const struct ctype_methods ctype_methods_libc_utf8 = {
 	.strlower = strlower_libc_mb,
 	.strtitle = strtitle_libc_mb,
 	.strupper = strupper_libc_mb,
+	/* in libc, casefolding is the same as lowercasing */
+	.strfold = strlower_libc_mb,
 	.wc_isdigit = wc_isdigit_libc_mb,
 	.wc_isalpha = wc_isalpha_libc_mb,
 	.wc_isalnum = wc_isalnum_libc_mb,