implement uchar.h (C11 UTF-16/32 conversion) interfaces

src/multibyte/c16rtomb.c

@@ -0,0 +1,33 @@
+#include <uchar.h>
+#include <errno.h>
+#include <wchar.h>
+
+size_t c16rtomb(char *restrict s, char16_t c16, mbstate_t *restrict ps)
+{
+	unsigned *x = (unsigned *)ps;
+	wchar_t wc;
+
+	if (!s) {
+		if (*x) goto ilseq;
+		return 1;
+	}
+
+	if (!*x && c16 - 0xd800u < 0x400) {
+		*x = c16 - 0xd7c0 << 10;
+		return 0;
+	}
+
+	if (*x) {
+		if (c16 - 0xdc00u >= 0x400) goto ilseq;
+		else wc = *x + c16 - 0xdc00;
+		*x = 0;
+	} else {
+		wc = c16;
+	}
+	return wcrtomb(s, wc, 0);
+
+ilseq:
+	*x = 0;
+	errno = EILSEQ;
+	return -1;
+}

src/multibyte/c32rtomb.c

@@ -0,0 +1,7 @@
+#include <uchar.h>
+#include <wchar.h>
+
+size_t c32rtomb(char *restrict s, char32_t c32, mbstate_t *restrict ps)
+{
+	return wcrtomb(s, c32, ps);
+}

src/multibyte/mbrtoc16.c

@@ -0,0 +1,28 @@
+#include <uchar.h>
+#include <wchar.h>
+
+size_t mbrtoc16(char16_t *restrict pc16, const char *restrict s, size_t n, mbstate_t *restrict ps)
+{
+	unsigned *pending = (unsigned *)ps;
+
+	if (!s) return mbrtoc16(0, "", 1, ps);
+
+	/* mbrtowc states for partial UTF-8 characters have the high bit set;
+	 * we use nonzero states without high bit for pending surrogates. */
+	if ((int)*pending > 0) {
+ 		if (pc16) *pc16 = *pending;
+		*pending = 0;
+		return -3;
+	}
+
+	wchar_t wc;
+	size_t ret = mbrtowc(&wc, s, n, ps);
+	if (ret <= 4) {
+		if (wc >= 0x10000) {
+			*pending = (wc & 0x3ff) + 0xdc00;
+			wc = 0xd7c0 + (wc >> 10);
+		}
+		if (pc16) *pc16 = wc;
+	}
+	return ret;
+}

src/multibyte/mbrtoc32.c

@@ -0,0 +1,11 @@
+#include <uchar.h>
+#include <wchar.h>
+
+size_t mbrtoc32(char32_t *restrict pc32, const char *restrict s, size_t n, mbstate_t *restrict ps)
+{
+	if (!s) return mbrtoc32(0, "", 1, ps);
+	wchar_t wc;
+	size_t ret = mbrtowc(&wc, s, n, ps);
+	if (ret <= 4 && pc32) *pc32 = wc;
+	return ret;
+}