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const std = @import("std");
/// `CodePoint` represents a Unicode code point by its code,
/// length, and offset in the source bytes.
pub const CodePoint = struct {
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.
pub const Iterator = struct {
bytes: []const u8,
i: u32 = 0,
pub fn next(self: *Iterator) ?CodePoint {
if (self.i >= self.bytes.len) return null;
if (self.bytes[self.i] < 128) {
// ASCII fast path
defer self.i += 1;
return .{ .len = 1, .offset = self.i };
}
const cp = CodePoint{
.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."),
},
.offset = self.i,
};
self.i += cp.len;
return cp;
}
pub fn peek(self: *Iterator) ?CodePoint {
const saved_i = self.i;
defer self.i = saved_i;
return self.next();
}
};
test "peek" {
const src = "Hi";
var iter = Iterator{ .bytes = src };
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(?CodePoint, null), iter.peek());
try std.testing.expectEqual(@as(?CodePoint, null), iter.next());
}
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