From 08be45bfeb85bc809a492b9d0147052a028dd8ec Mon Sep 17 00:00:00 2001
From: Jose Colon Rodriguez
Date: Sun, 18 Feb 2024 11:21:49 -0400
Subject: Back to zg code_point. 4ms faster than Ghostty's Utf8Decoder

---
 src/code_point.zig | 68 +++++++++++++++++++++++++++++++-----------------------
 1 file changed, 39 insertions(+), 29 deletions(-)

(limited to 'src/code_point.zig')

diff --git a/src/code_point.zig b/src/code_point.zig
index 098e635..ac37562 100644
--- a/src/code_point.zig
+++ b/src/code_point.zig
@@ -3,29 +3,9 @@ const std = @import("std");
 /// `CodePoint` represents a Unicode code point by its code,
 /// length, and offset in the source bytes.
 pub const CodePoint = struct {
+    code: u21,
     len: u3,
     offset: u32,
-
-    pub fn code(self: CodePoint, src: []const u8) u21 {
-        const cp_bytes = src[self.offset..][0..self.len];
-
-        return switch (self.len) {
-            1 => cp_bytes[0],
-
-            2 => (@as(u21, (cp_bytes[0] & 0b00011111)) << 6) | (cp_bytes[1] & 0b00111111),
-
-            3 => (((@as(u21, (cp_bytes[0] & 0b00001111)) << 6) |
-                (cp_bytes[1] & 0b00111111)) << 6) |
-                (cp_bytes[2] & 0b00111111),
-
-            4 => (((((@as(u21, (cp_bytes[0] & 0b00000111)) << 6) |
-                (cp_bytes[1] & 0b00111111)) << 6) |
-                (cp_bytes[2] & 0b00111111)) << 6) |
-                (cp_bytes[3] & 0b00111111),
-
-            else => @panic("code_point.CodePoint.code: Invalid code point length."),
-        };
-    }
 };
 
 /// `Iterator` iterates a string one `CodePoint` at-a-time.
@@ -39,20 +19,51 @@ pub const Iterator = struct {
         if (self.bytes[self.i] < 128) {
             // ASCII fast path
             defer self.i += 1;
-            return .{ .len = 1, .offset = self.i };
+
+            return .{
+                .code = self.bytes[self.i],
+                .len = 1,
+                .offset = self.i,
+            };
         }
 
-        const cp = CodePoint{
+        var cp = CodePoint{
+            .code = undefined,
             .len = switch (self.bytes[self.i]) {
                 0b1100_0000...0b1101_1111 => 2,
                 0b1110_0000...0b1110_1111 => 3,
                 0b1111_0000...0b1111_0111 => 4,
-                else => @panic("code_point.Iterator.next: Invalid start byte."),
+                else => {
+                    defer self.i += 1;
+                    // Unicode replacement code point.
+                    return .{
+                        .code = 0xfffd,
+                        .len = 1,
+                        .offset = self.i,
+                    };
+                },
             },
             .offset = self.i,
         };
 
+        const cp_bytes = self.bytes[self.i..][0..cp.len];
         self.i += cp.len;
+
+        cp.code = switch (cp.len) {
+            2 => (@as(u21, (cp_bytes[0] & 0b00011111)) << 6) | (cp_bytes[1] & 0b00111111),
+
+            3 => (((@as(u21, (cp_bytes[0] & 0b00001111)) << 6) |
+                (cp_bytes[1] & 0b00111111)) << 6) |
+                (cp_bytes[2] & 0b00111111),
+
+            4 => (((((@as(u21, (cp_bytes[0] & 0b00000111)) << 6) |
+                (cp_bytes[1] & 0b00111111)) << 6) |
+                (cp_bytes[2] & 0b00111111)) << 6) |
+                (cp_bytes[3] & 0b00111111),
+
+            else => @panic("CodePointIterator.next invalid code point length."),
+        };
+
         return cp;
     }
 
@@ -64,12 +75,11 @@ pub const Iterator = struct {
 };
 
 test "peek" {
-    const src = "Hi";
-    var iter = Iterator{ .bytes = src };
+    var iter = Iterator{ .bytes = "Hi" };
 
-    try std.testing.expectEqual(@as(u21, 'H'), iter.next().?.code(src));
-    try std.testing.expectEqual(@as(u21, 'i'), iter.peek().?.code(src));
-    try std.testing.expectEqual(@as(u21, 'i'), iter.next().?.code(src));
+    try std.testing.expectEqual(@as(u21, 'H'), iter.next().?.code);
+    try std.testing.expectEqual(@as(u21, 'i'), iter.peek().?.code);
+    try std.testing.expectEqual(@as(u21, 'i'), iter.next().?.code);
     try std.testing.expectEqual(@as(?CodePoint, null), iter.peek());
     try std.testing.expectEqual(@as(?CodePoint, null), iter.next());
 }
-- 
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