Wrote the new attributed string system's grapheme code for OS X.

darwin/graphemes.m

@@ -0,0 +1,58 @@
+// 3 december 2016
+#import "uipriv_darwin.h"
+
+// CFStringGetRangeOfComposedCharactersAtIndex() is the function for grapheme clusters
+// https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/Strings/Articles/stringsClusters.html says that this does work on all multi-codepoint graphemes (despite the name), and that this is the preferred function for this particular job anyway
+
+int graphemesTakesUTF16(void)
+{
+	return 1;
+}
+
+struct graphemes *graphemes(void *s, size_t len)
+{
+	struct graphemes *g;
+	UniChar *str = (UniChar *) s;
+	CFString cfstr;
+	size_t ppos, gpos;
+	CFRange range;
+	size_t i;
+
+	g = uiNew(struct graphemes);
+
+	cfstr = CFStringCreateWithCharactersNoCopy(NULL, str, len, kCFAllocatorNull);
+	if (cfstr == NULL) {
+		// TODO
+	}
+
+	// first figure out how many graphemes there are
+	g->len = 0;
+	ppos = 0;
+	while (ppos < len) {
+		range = CFStringGetRangeOfComposedCharactersAtIndex(cfstr, ppos);
+		g->len++;
+		ppos = range.location + range.length;
+	}
+
+	g->pointsToGraphemes = (size_t *) uiAlloc((len + 1) * sizeof (size_t), "size_t[] (graphemes)");
+	g->graphemesToPoints = (size_t *) uiAlloc((g->len + 1) * sizeof (size_t), "size_t[] (graphemes)");
+
+	// now calculate everything
+	// fortunately due to the use of CFRange we can do this in one loop trivially!
+	ppos = 0;
+	gpos = 0;
+	while (ppos < len) {
+		range = CFStringGetRangeOfComposedCharactersAtIndex(cfstr, ppos);
+		for (i = 0; i < range.length; i++)
+			g->pointsToGraphemes[range.location + i] = gpos;
+		g->graphemesToPoints[gpos] = range.location;
+		gpos++;
+		ppos = range.location + range.length;
+	}
+	// and set the last one
+	g->pointsToGraphemes[ppos] = gpos;
+	g->graphemesToPoints[gpos] = ppos;
+
+	CFRelease(cfstr);
+	return g;
+}