std.fmt.hex: support more integer sizes

Fixes ziglang#23799

Author: myclevorname

lib/std/fmt.zig

@@ -2758,11 +2758,11 @@ pub const hex_charset = "0123456789abcdef";
 
 /// Converts an unsigned integer of any multiple of u8 to an array of lowercase
 /// hex bytes, little endian.
-pub fn hex(x: anytype) [@sizeOf(@TypeOf(x)) * 2]u8 {
+pub fn hex(x: anytype) [2 * @divExact(@typeInfo(@TypeOf(x)).int.bits, 8)]u8 {
     comptime assert(@typeInfo(@TypeOf(x)).int.signedness == .unsigned);
-    var result: [@sizeOf(@TypeOf(x)) * 2]u8 = undefined;
-    var i: usize = 0;
-    while (i < result.len / 2) : (i += 1) {
+    const octet_count = @typeInfo(@TypeOf(x)).int.bits / 8;
+    var result: [2 * octet_count]u8 = undefined;
+    for (0..octet_count) |i| {
         const byte: u8 = @truncate(x >> @intCast(8 * i));
         result[i * 2 + 0] = hex_charset[byte >> 4];
         result[i * 2 + 1] = hex_charset[byte & 15];
@@ -2771,6 +2771,11 @@ pub fn hex(x: anytype) [@sizeOf(@TypeOf(x)) * 2]u8 {
 }
 
 test hex {
+    {
+        const x = hex(@as(u48, 0x1234_5678_3210));
+        try std.testing.expect(x.len == 12);
+        try std.testing.expectEqualStrings("103278563412", &x);
+    }
     {
         const x = hex(@as(u32, 0xdeadbeef));
         try std.testing.expect(x.len == 8);