Zig: completed Luhn

zig/luhn/.exercism/config.json

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+{
+  "authors": [
+    "ee7"
+  ],
+  "files": {
+    "solution": [
+      "luhn.zig"
+    ],
+    "test": [
+      "test_luhn.zig"
+    ],
+    "example": [
+      ".meta/example.zig"
+    ]
+  },
+  "blurb": "Given a number determine whether or not it is valid per the Luhn formula.",
+  "source": "The Luhn Algorithm on Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Luhn_algorithm"
+}

zig/luhn/.exercism/metadata.json

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+{"track":"zig","exercise":"luhn","id":"5c3683c495e143e98cf457b99607c9fb","url":"https://exercism.org/tracks/zig/exercises/luhn","handle":"Chomp1295","is_requester":true,"auto_approve":false}

zig/luhn/HELP.md

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+# Help
+
+## Running the tests
+
+Write your code in `<exercise_name>.zig`.
+
+To run the tests for an exercise, run:
+
+```bash
+zig test test_exercise_name.zig
+```
+
+in the exercise's root directory (replacing `exercise_name` with the name of the exercise).
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit luhn.zig` command.
+This command will upload your solution to the Exercism website and print the solution page's URL.
+
+It's possible to submit an incomplete solution which allows you to:
+
+- See how others have completed the exercise
+- Request help from a mentor
+
+## Need to get help?
+
+If you'd like help solving the exercise, check the following pages:
+
+- The [Zig track's documentation](https://exercism.org/docs/tracks/zig)
+- The [Zig track's programming category on the forum](https://forum.exercism.org/c/programming/zig)
+- [Exercism's programming category on the forum](https://forum.exercism.org/c/programming/5)
+- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
+
+Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
+
+- [The Zig Programming Language Documentation][documentation] is a great overview of all of the language features that Zig provides to those who use it.
+- [Zig Guide][zig-guide] is an excellent primer that explains the language features that Zig has to offer.
+- [Ziglings][ziglings] is highly recommended.
+  Learn Zig by fixing tiny broken programs.
+- [The Zig Programming Language Discord][discord-zig] is the main [Discord][discord].
+  It provides a great way to get in touch with the Zig community at large, and get some quick, direct help for any Zig related problem.
+- [#zig][irc] on irc.freenode.net is the main Zig IRC channel.
+- [/r/Zig][reddit] is the main Zig subreddit.
+- [Stack Overflow][stack-overflow] can be used to discover code snippets and solutions to problems that may have already asked and maybe solved by others.
+
+[discord]: https://discordapp.com
+[discord-zig]: https://discord.com/invite/gxsFFjE
+[documentation]: https://ziglang.org/documentation/master
+[irc]: https://webchat.freenode.net/?channels=%23zig
+[reddit]: https://www.reddit.com/r/Zig
+[stack-overflow]: https://stackoverflow.com/questions/tagged/zig
+[zig-guide]: https://zig.guide/
+[ziglings]: https://codeberg.org/ziglings/exercises

zig/luhn/README.md

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+# Luhn
+
+Welcome to Luhn on Exercism's Zig Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+
+## Instructions
+
+Given a number determine whether or not it is valid per the Luhn formula.
+
+The [Luhn algorithm][luhn] is a simple checksum formula used to validate a variety of identification numbers, such as credit card numbers and Canadian Social Insurance Numbers.
+
+The task is to check if a given string is valid.
+
+## Validating a Number
+
+Strings of length 1 or less are not valid.
+Spaces are allowed in the input, but they should be stripped before checking.
+All other non-digit characters are disallowed.
+
+### Example 1: valid credit card number
+
+```text
+4539 3195 0343 6467
+```
+
+The first step of the Luhn algorithm is to double every second digit, starting from the right.
+We will be doubling
+
+```text
+4_3_ 3_9_ 0_4_ 6_6_
+```
+
+If doubling the number results in a number greater than 9 then subtract 9 from the product.
+The results of our doubling:
+
+```text
+8569 6195 0383 3437
+```
+
+Then sum all of the digits:
+
+```text
+8+5+6+9+6+1+9+5+0+3+8+3+3+4+3+7 = 80
+```
+
+If the sum is evenly divisible by 10, then the number is valid.
+This number is valid!
+
+### Example 2: invalid credit card number
+
+```text
+8273 1232 7352 0569
+```
+
+Double the second digits, starting from the right
+
+```text
+7253 2262 5312 0539
+```
+
+Sum the digits
+
+```text
+7+2+5+3+2+2+6+2+5+3+1+2+0+5+3+9 = 57
+```
+
+57 is not evenly divisible by 10, so this number is not valid.
+
+[luhn]: https://en.wikipedia.org/wiki/Luhn_algorithm
+
+## Source
+
+### Created by
+
+- @ee7
+
+### Based on
+
+The Luhn Algorithm on Wikipedia - https://en.wikipedia.org/wiki/Luhn_algorithm

zig/luhn/luhn.zig

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+const std = @import("std");
+const ascii = std.ascii;
+
+pub fn isValid(s: []const u8) bool {
+    var idx: usize = s.len;
+    var luhn_idx: usize = 1;
+    var total: u64 = 0;
+
+    while (idx > 0) {
+        idx -= 1;
+        if (s[idx] == 32) continue;
+        if (!ascii.isDigit(s[idx])) {
+            return false;
+        }
+
+        var curr: u8 = s[idx] - 48;
+        if (luhn_idx % 2 == 0) {
+            curr *= 2;
+            if (curr > 9) {
+                curr -= 9;
+            }
+        }
+        total += curr;
+        luhn_idx += 1;
+    }
+
+    if (luhn_idx <= 2) return false;
+    return total % 10 == 0;
+}

zig/luhn/test_luhn.zig

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+const std = @import("std");
+const testing = std.testing;
+
+const isValid = @import("luhn.zig").isValid;
+
+test "single digit strings cannot be valid" {
+    try testing.expect(!isValid("1"));
+}
+
+test "a single zero is invalid" {
+    try testing.expect(!isValid("0"));
+}
+
+test "a simple valid SIN that remains valid if reversed" {
+    try testing.expect(isValid("059"));
+}
+
+test "a simple valid SIN that becomes invalid if reversed" {
+    try testing.expect(isValid("59"));
+}
+
+test "a valid Canadian SIN" {
+    try testing.expect(isValid("055 444 285"));
+}
+
+test "invalid Canadian SIN" {
+    try testing.expect(!isValid("055 444 286"));
+}
+
+test "invalid credit card" {
+    try testing.expect(!isValid("8273 1232 7352 0569"));
+}
+
+test "invalid long number with an even remainder" {
+    try testing.expect(!isValid("1 2345 6789 1234 5678 9012"));
+}
+
+test "invalid long number with a remainder divisible by 5" {
+    try testing.expect(!isValid("1 2345 6789 1234 5678 9013"));
+}
+
+test "valid number with an even number of digits" {
+    try testing.expect(isValid("095 245 88"));
+}
+
+test "valid number with an odd number of spaces" {
+    try testing.expect(isValid("234 567 891 234"));
+}
+
+test "valid strings with a non-digit added at the end become invalid" {
+    try testing.expect(!isValid("059a"));
+}
+
+test "valid strings with punctuation included become invalid" {
+    try testing.expect(!isValid("055-444-285"));
+}
+
+test "valid strings with symbols included become invalid" {
+    try testing.expect(!isValid("055# 444$ 285"));
+}
+
+test "single zero with space is invalid" {
+    try testing.expect(!isValid(" 0"));
+}
+
+test "more than a single zero is valid" {
+    try testing.expect(isValid("0000 0"));
+}
+
+test "input digit 9 is correctly converted to output digit 9" {
+    try testing.expect(isValid("091"));
+}
+
+test "very long input is valid" {
+    try testing.expect(isValid("9999999999 9999999999 9999999999 9999999999"));
+}
+
+test "valid luhn with an odd number of digits and non zero first digit" {
+    try testing.expect(isValid("109"));
+}
+
+test "using ascii value for non-doubled non-digit isn't allowed" {
+    try testing.expect(!isValid("055b 444 285"));
+}
+
+test "using ascii value for doubled non-digit isn't allowed" {
+    try testing.expect(!isValid(":9"));
+}
+
+test "non-numeric, non-space char in the middle with a sum that's divisible by 10 isn't allowed" {
+    try testing.expect(!isValid("59%59"));
+}