1const std = @import("std");
 2const maxInt = std.math.maxInt;
 3
 4pub fn parseU64(buf: []const u8, radix: u8) !u64 {
 5    var x: u64 = 0;
 6
 7    for (buf) |c| {
 8        const digit = charToDigit(c);
 9
10        if (digit >= radix) {
11            return error.InvalidChar;
12        }
13
14        // x *= radix
15        var ov = @mulWithOverflow(x, radix);
16        if (ov[1] != 0) return error.OverFlow;
17
18        // x += digit
19        ov = @addWithOverflow(ov[0], digit);
20        if (ov[1] != 0) return error.OverFlow;
21        x = ov[0];
22    }
23
24    return x;
25}
26
27fn charToDigit(c: u8) u8 {
28    return switch (c) {
29        '0'...'9' => c - '0',
30        'A'...'Z' => c - 'A' + 10,
31        'a'...'z' => c - 'a' + 10,
32        else => maxInt(u8),
33    };
34}
35
36test "parse u64" {
37    const result = try parseU64("1234", 10);
38    try std.testing.expect(result == 1234);
39}
40
41// test