From 7e4cc4641e966a1aa32fa021a9476af3b9813485 Mon Sep 17 00:00:00 2001
From: Sam Atman
Date: Tue, 13 May 2025 13:38:28 -0400
Subject: Various small iterator improvements

---
 src/code_point.zig | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 51 insertions(+), 4 deletions(-)

(limited to 'src/code_point.zig')

diff --git a/src/code_point.zig b/src/code_point.zig
index a319d36..b3c9aea 100644
--- a/src/code_point.zig
+++ b/src/code_point.zig
@@ -48,12 +48,22 @@ pub fn decodeAtCursor(bytes: []const u8, cursor: *u32) ?CodePoint {
     };
     // Multibyte
 
+<<<<<<< HEAD
     // Second:
     var class: u4 = @intCast(u8dfa[byte]);
     var st: u32 = state_dfa[class];
     if (st == RUNE_REJECT or cursor.* == bytes.len) {
         @branchHint(.cold);
         // First one is never a truncation
+||||||| parent of ad4b046 (Various small iterator improvements)
+    // Return replacement if we don' have a complete codepoint remaining. Consumes only one byte
+    if (cp.len > bytes.len) {
+        // Unicode replacement code point.
+=======
+    // Return replacement if we don't have a complete codepoint remaining. Consumes only one byte.
+    if (cp.len > bytes.len) {
+        // Unicode replacement code point.
+>>>>>>> ad4b046 (Various small iterator improvements)
         return .{
             .code = 0xfffd,
             .len = 1,
@@ -158,10 +168,19 @@ pub const Iterator = struct {
         return decodeAtCursor(self.bytes, &self.i);
     }
 
-    pub fn peek(self: *Iterator) ?CodePoint {
-        const saved_i = self.i;
-        defer self.i = saved_i;
-        return self.next();
+    pub fn peek(iter: *Iterator) ?CodePoint {
+        const saved_i = iter.i;
+        defer iter.i = saved_i;
+        return iter.next();
+    }
+
+    /// Create a backward iterator at this point.  It will repeat
+    /// the last CodePoint seen.
+    pub fn reverseIterator(iter: *Iterator) ReverseIterator {
+        if (iter.i == iter.bytes.len) {
+            return .init(iter.bytes);
+        }
+        return .{ .i = iter.i, .bytes = iter.bytes };
     }
 };
 
@@ -266,6 +285,17 @@ pub const ReverseIterator = struct {
         defer iter.i = saved_i;
         return iter.prev();
     }
+
+    /// Create a forward iterator at this point.  It will repeat the
+    /// last CodePoint seen.
+    pub fn forwardIterator(iter: *ReverseIterator) Iterator {
+        if (iter.i) |i| {
+            var fwd: Iterator = .{ .i = i, .bytes = iter.bytes };
+            _ = fwd.next();
+            return fwd;
+        }
+        return .{ .i = 0, .bytes = iter.bytes };
+    }
 };
 
 inline fn followbyte(b: u8) bool {
@@ -410,6 +440,23 @@ test ReverseIterator {
         try testing.expectEqual(@as(?CodePoint, null), r_iter.prev());
         try testing.expectEqual(@as(?CodePoint, null), r_iter.prev());
     }
+    {
+        var r_iter: ReverseIterator = .init("123");
+        try testing.expectEqual(@as(u21, '3'), r_iter.prev().?.code);
+        try testing.expectEqual(@as(u21, '2'), r_iter.prev().?.code);
+        try testing.expectEqual(@as(u21, '1'), r_iter.prev().?.code);
+        var iter = r_iter.forwardIterator();
+        try testing.expectEqual(@as(u21, '1'), iter.next().?.code);
+        try testing.expectEqual(@as(u21, '2'), iter.next().?.code);
+        try testing.expectEqual(@as(u21, '3'), iter.next().?.code);
+        r_iter = iter.reverseIterator();
+        try testing.expectEqual(@as(u21, '3'), r_iter.prev().?.code);
+        try testing.expectEqual(@as(u21, '2'), r_iter.prev().?.code);
+        iter = r_iter.forwardIterator();
+        r_iter = iter.reverseIterator();
+        try testing.expectEqual(@as(u21, '2'), iter.next().?.code);
+        try testing.expectEqual(@as(u21, '2'), r_iter.prev().?.code);
+    }
 }
 
 const std = @import("std");
-- 
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