1 files changed, 37 insertions, 0 deletions
diff --git a/vendor/librune/lib/utf8/u8prev.c b/vendor/librune/lib/utf8/u8prev.c
new file mode 100644
index 0000000..fac0fc7
--- /dev/null
+++ b/vendor/librune/lib/utf8/u8prev.c
@@ -0,0 +1,37 @@
+#include "rune.h"
+#include "utf8.h"
+
+#include "internal/common.h"
+
+const char8_t *
+u8prev(rune *ch, const char8_t **p, const char8_t *start)
+{
+	int off;
+	bool match = true;
+	const char8_t *s = *p;
+	ptrdiff_t d = s - start;
+
+	if (d <= 0) {
+		return nullptr;
+	} else if (U1(s[-1])) {
+		*ch = s[-1];
+		off = 1;
+	} else if (d > 1 && UC(s[-1]) && U2(s[-2])) {
+		*ch = ((s[-2] & 0x1F) << 6) | (s[-1] & 0x3F);
+		off = 2;
+	} else if (d > 2 && UC(s[-1]) && UC(s[-2]) && U3(s[-3])) {
+		*ch = ((s[-3] & 0x0F) << 12) | ((s[-2] & 0x3F) << 6) | (s[-1] & 0x3F);
+		off = 3;
+	} else if (d > 3 && UC(s[-1]) && UC(s[-2]) && UC(s[-3]) && U4(s[-4])) {
+		*ch = ((s[-4] & 0x07) << 18) | ((s[-3] & 0x3F) << 12)
+		    | ((s[-2] & 0x3F) << 6) | (s[-1] & 0x3F);
+		off = 4;
+	} else
+		match = false;
+
+	if (match && u8chkr(*ch))
+		return *p -= off;
+
+	*ch = RUNE_ERROR;
+	return *p--;
+}