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log10_int

Return the log base 10 of integer value x, rounding down to the nearest integer.

log10.log10_int

pub fn log10_int(x: anytype) std.math.Log2Int(@TypeOf(x))

File

lib/std/math/log10.zig:42

Code

pub fn log10_int(x: anytype) std.math.Log2Int(@TypeOf(x)) {
    const T = @TypeOf(x);
    const OutT = std.math.Log2Int(T);
    if (@typeInfo(T) != .int or @typeInfo(T).int.signedness != .unsigned)
        @compileError("log10_int requires an unsigned integer, found " ++ @typeName(T));

    std.debug.assert(x != 0);

    const bit_size = @typeInfo(T).int.bits;

    if (bit_size <= 8) {
        return @as(OutT, @intCast(log10_int_u8(x)));
    } else if (bit_size <= 16) {
        return @as(OutT, @intCast(less_than_5(x)));
    }

    var val = x;
    var log: u32 = 0;

    inline for (0..11) |i| {
        // Unnecessary branches should be removed by the compiler
        if (bit_size > (1 << (11 - i)) * 5 * @log2(10.0) and val >= pow10((1 << (11 - i)) * 5)) {
            const num_digits = (1 << (11 - i)) * 5;
            val /= pow10(num_digits);
            log += num_digits;
        }
    }

    if (val >= pow10(5)) {
        val /= pow10(5);
        log += 5;
    }

    return @as(OutT, @intCast(log + less_than_5(@as(u32, @intCast(val)))));
}