28 lines
1.0 KiB
Zig
28 lines
1.0 KiB
Zig
pub fn factorial(comptime Num: type, n: i8) ?Num {
|
|
return if (@typeInfo(Num) != .Int)
|
|
@compileError("factorial called with non-integral type: " ++ @typeName(Num))
|
|
else if (n < 0)
|
|
null
|
|
else calc: {
|
|
var i: i8 = 1;
|
|
var fac: Num = 1;
|
|
while (i <= n) : (i += 1) {
|
|
const tmp = @mulWithOverflow(fac, i);
|
|
if (tmp[1] != 0)
|
|
break :calc null; // overflow
|
|
fac = tmp[0];
|
|
} else break :calc fac;
|
|
};
|
|
}
|
|
|
|
pub fn main() !void {
|
|
const stdout = @import("std").io.getStdOut().writer();
|
|
|
|
try stdout.print("-1! = {?}\n", .{factorial(i32, -1)});
|
|
try stdout.print("0! = {?}\n", .{factorial(i32, 0)});
|
|
try stdout.print("5! = {?}\n", .{factorial(i32, 5)});
|
|
try stdout.print("33!(64 bit) = {?}\n", .{factorial(i64, 33)}); // not valid i64 factorial
|
|
try stdout.print("33! = {?}\n", .{factorial(i128, 33)}); // biggest i128 factorial possible
|
|
try stdout.print("34! = {?}\n", .{factorial(i128, 34)}); // will overflow
|
|
}
|