From acf3cdcf80da7c3443e202a02d4b626c13e9e8dd Mon Sep 17 00:00:00 2001
From: default <nobody@localhost>
Date: Fri, 17 Nov 2023 03:51:04 +0100
Subject: Backport from xs.

---
 xs_unicode.h | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

(limited to 'xs_unicode.h')

diff --git a/xs_unicode.h b/xs_unicode.h
index c7d6190..f5880f0 100644
--- a/xs_unicode.h
+++ b/xs_unicode.h
@@ -8,6 +8,9 @@
  xs_str *xs_utf8_enc(xs_str *str, unsigned int cpoint);
  unsigned int xs_utf8_dec(char **str);
  int xs_unicode_width(unsigned int cpoint);
+ int xs_is_surrogate(unsigned int cpoint);
+ unsigned int xs_surrogate_dec(unsigned int p1, unsigned int p2);
+ unsigned int xs_surrogate_enc(unsigned int cpoint);
  unsigned int *_xs_unicode_upper_search(unsigned int cpoint);
  unsigned int *_xs_unicode_lower_search(unsigned int cpoint);
  #define xs_unicode_is_upper(cpoint) (!!_xs_unicode_upper_search(cpoint))
@@ -138,6 +141,32 @@ int xs_unicode_width(unsigned int cpoint)
 }
 
 
+/** surrogate pairs **/
+
+int xs_is_surrogate(unsigned int cpoint)
+/* checks if cpoint is the first element of a Unicode surrogate pair */
+{
+    return cpoint >= 0xd800 && cpoint <= 0xdfff;
+}
+
+
+unsigned int xs_surrogate_dec(unsigned int p1, unsigned int p2)
+/* "decodes" a surrogate pair into a codepoint */
+{
+    return 0x10000 | ((p1 & 0x3ff) << 10) | (p2 & 0x3ff);
+}
+
+
+unsigned int xs_surrogate_enc(unsigned int cpoint)
+/* "encodes" a Unicode into a surrogate pair (p1 in the MSB word) */
+{
+    unsigned int p1 = 0xd7c0 + (cpoint >> 10);
+    unsigned int p2 = 0xdc00 + (cpoint & 0x3ff);
+
+    return (p1 << 16) | p2;
+}
+
+
 #ifdef _XS_UNICODE_TBL_H
 
 /* include xs_unicode_tbl.h before this one to use these functions */
-- 
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