1 files changed, 48 insertions, 0 deletions
diff --git a/src/detab.c b/src/detab.c
new file mode 100644
index 0000000..e03fcf7
--- /dev/null
+++ b/src/detab.c
@@ -0,0 +1,48 @@
+#include "bstrlib.h"
+
+// UTF-8 aware detab:  assumes s has no newlines, or only a final newline.
+// Return 0 on success, BSTR_ERR if invalid UTF-8.
+extern int bdetab(bstring s, int utf8)
+{
+  unsigned char c;
+  int pos = 0;  // a count of characters
+  int byte = 0; // a count of bytes
+  int high_chars_to_skip = 0;
+  int numspaces = 0;
+  while ((c = bchar(s, byte))) {
+    if (utf8 && high_chars_to_skip > 0) {
+      if (c >= 0x80) {
+        high_chars_to_skip--;
+        byte++;
+      } else {
+        return BSTR_ERR; // invalid utf-8
+      }
+    } else if (c == '\t') {
+      bdelete(s, byte, 1); // delete tab character
+      numspaces = 4 - (pos % 4);
+      binsertch(s, byte, numspaces, ' ');
+      byte += numspaces;
+      pos  += numspaces;
+    } else if (c <= 0x80 || !utf8) {
+      byte++;
+      pos++;
+    } else {  // multibyte utf8 sequences
+      if (c >> 1 == 0176) {
+        high_chars_to_skip = 5;
+      } else if (c >> 2 == 076) {
+        high_chars_to_skip = 4;
+      } else if (c >> 3 == 036) {
+        high_chars_to_skip = 3;
+      } else if (c >> 4 == 016) {
+        high_chars_to_skip = 2;
+      } else if (c >> 5 == 06) {
+        high_chars_to_skip = 1;
+      } else {
+        return BSTR_ERR; // invalid utf-8
+      }
+      pos++;
+      byte++;
+    }
+  }
+  return 0;
+}