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authorRich Felker <dalias@aerifal.cx>2013-04-08 23:01:32 -0400
committerRich Felker <dalias@aerifal.cx>2013-04-08 23:01:32 -0400
commitea34b1b90ca5ba3b87725662f6a1ff03b7a88a1f (patch)
treef9289a7c3a981755b54860555a65a6afde26ba72 /src/multibyte/mbtowc.c
parenta49e038bab7b3927b6a9c7d0c52f9e1a9cb82629 (diff)
downloadmusl-ea34b1b90ca5ba3b87725662f6a1ff03b7a88a1f.tar.gz
implement mbtowc directly, not as a wrapper for mbrtowc
the interface contract for mbtowc admits a much faster implementation than mbrtowc can achieve; wrapping mbrtowc with an extra call frame only made the situation worse. since the regex implementation uses mbtowc already, this change should improve regex performance too. it may be possible to improve performance in other places internally by switching from mbrtowc to mbtowc.
Diffstat (limited to 'src/multibyte/mbtowc.c')
-rw-r--r--src/multibyte/mbtowc.c44
1 files changed, 39 insertions, 5 deletions
diff --git a/src/multibyte/mbtowc.c b/src/multibyte/mbtowc.c
index b5dd7e3c..ec9e54ad 100644
--- a/src/multibyte/mbtowc.c
+++ b/src/multibyte/mbtowc.c
@@ -10,10 +10,44 @@
#include <errno.h>
#include "internal.h"
-
-int mbtowc(wchar_t *restrict wc, const char *restrict s, size_t n)
+#include <stdio.h>
+int mbtowc(wchar_t *restrict wc, const char *restrict src, size_t n)
{
- mbstate_t st = { 0 };
- n = mbrtowc(wc, s, n, &st);
- return n+2 ? n : -1;
+ unsigned c;
+ const unsigned char *s = (const void *)src;
+
+ if (!s) return 0;
+ if (!n) goto ilseq;
+ if (!wc) wc = (void *)&wc;
+
+ if (*s < 0x80) return !!(*wc = *s);
+ if (*s-SA > SB-SA) goto ilseq;
+ c = bittab[*s++-SA];
+
+ /* Avoid excessive checks against n: If shifting the state n-1
+ * times does not clear the high bit, then the value of n is
+ * insufficient to read a character */
+ if (n<4 && ((c<<(6*n-6)) & (1U<<31))) goto ilseq;
+
+ if (OOB(c,*s)) goto ilseq;
+ c = c<<6 | *s++-0x80;
+ if (!(c&(1U<<31))) {
+ *wc = c;
+ return 2;
+ }
+
+ if (*s-0x80u >= 0x40) goto ilseq;
+ c = c<<6 | *s++-0x80;
+ if (!(c&(1U<<31))) {
+ *wc = c;
+ return 3;
+ }
+
+ if (*s-0x80u >= 0x40) goto ilseq;
+ *wc = c<<6 | *s++-0x80;
+ return 4;
+
+ilseq:
+ errno = EILSEQ;
+ return -1;
}