Add fast paths for conversion of plain ASCII characters.

1 files changed, 13 insertions, 0 deletions

diff --git a/lib/libc/locale/utf8.c b/lib/libc/locale/utf8.c
index c0fbcf47d22b..bab04f05ebb7 100644
--- a/lib/libc/locale/utf8.c
+++ b/lib/libc/locale/utf8.c
@@ -90,6 +90,13 @@ _UTF8_mbrtowc(wchar_t * __restrict pwc, const char * __restrict s, size_t n,
 		/* Incomplete multibyte sequence */
 		return ((size_t)-2);
 
+	if (us->want == 0 && ((ch = (unsigned char)*s) & ~0x7f) == 0) {
+		/* Fast path for plain ASCII characters. */
+		if (pwc != NULL)
+			*pwc = ch;
+		return (ch != '\0' ? 1 : 0);
+	}
+
 	if (us->want == 0) {
 		/*
 		 * Determine the number of octets that make up this character
@@ -198,6 +205,12 @@ _UTF8_wcrtomb(char * __restrict s, wchar_t wc, mbstate_t * __restrict ps)
 		/* Reset to initial shift state (no-op) */
 		return (1);
 
+	if ((wc & ~0x7f) == 0) {
+		/* Fast path for plain ASCII characters. */
+		*s = (char)wc;
+		return (1);
+	}
+
 	/*
 	 * Determine the number of octets needed to represent this character.
 	 * We always output the shortest sequence possible. Also specify the