aboutsummaryrefslogtreecommitdiff
path: root/vendor/librune/lib/utf8/u8prev.c
diff options
context:
space:
mode:
Diffstat (limited to 'vendor/librune/lib/utf8/u8prev.c')
-rw-r--r--vendor/librune/lib/utf8/u8prev.c37
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--;
+}