Function parseFloat [src]

Alias for std.fmt.parse_float.parseFloat

Prototype

pub fn parseFloat(comptime T: type, s: []const u8) ParseFloatError!T

Parameters

T: types: []const u8

Possible Errors

InvalidCharacter

Example

 test parseFloat {
    inline for ([_]type{ f16, f32, f64, f80, f128 }) |T| {
        try testing.expectError(error.InvalidCharacter, parseFloat(T, ""));
        try testing.expectError(error.InvalidCharacter, parseFloat(T, "   1"));
        try testing.expectError(error.InvalidCharacter, parseFloat(T, "1abc"));
        try testing.expectError(error.InvalidCharacter, parseFloat(T, "+"));
        try testing.expectError(error.InvalidCharacter, parseFloat(T, "-"));

        try expectEqual(try parseFloat(T, "0"), 0.0);
        try expectEqual(try parseFloat(T, "0"), 0.0);
        try expectEqual(try parseFloat(T, "+0"), 0.0);
        try expectEqual(try parseFloat(T, "-0"), 0.0);

        try expectEqual(try parseFloat(T, "0e0"), 0);
        try expectEqual(try parseFloat(T, "2e3"), 2000.0);
        try expectEqual(try parseFloat(T, "1e0"), 1.0);
        try expectEqual(try parseFloat(T, "-2e3"), -2000.0);
        try expectEqual(try parseFloat(T, "-1e0"), -1.0);
        try expectEqual(try parseFloat(T, "1.234e3"), 1234);

        try expect(approxEqAbs(T, try parseFloat(T, "3.141"), 3.141, epsilon));
        try expect(approxEqAbs(T, try parseFloat(T, "-3.141"), -3.141, epsilon));

        try expectEqual(try parseFloat(T, "1e-5000"), 0);
        try expectEqual(try parseFloat(T, "1e+5000"), std.math.inf(T));

        try expectEqual(try parseFloat(T, "0.4e0066999999999999999999999999999999999999999999999999999"), std.math.inf(T));
        try expect(approxEqAbs(T, try parseFloat(T, "0_1_2_3_4_5_6.7_8_9_0_0_0e0_0_1_0"), @as(T, 123456.789000e10), epsilon));

        // underscore rule is simple and reduces to "can only occur between two digits" and multiple are not supported.
        try expectError(error.InvalidCharacter, parseFloat(T, "0123456.789000e_0010")); // cannot occur immediately after exponent
        try expectError(error.InvalidCharacter, parseFloat(T, "_0123456.789000e0010")); // cannot occur before any digits
        try expectError(error.InvalidCharacter, parseFloat(T, "0__123456.789000e_0010")); // cannot occur twice in a row
        try expectError(error.InvalidCharacter, parseFloat(T, "0123456_.789000e0010")); // cannot occur before decimal point
        try expectError(error.InvalidCharacter, parseFloat(T, "0123456.789000e0010_")); // cannot occur at end of number

        try expect(approxEqAbs(T, try parseFloat(T, "1e-2"), 0.01, epsilon));
        try expect(approxEqAbs(T, try parseFloat(T, "1234e-2"), 12.34, epsilon));

        try expect(approxEqAbs(T, try parseFloat(T, "1."), 1, epsilon));
        try expect(approxEqAbs(T, try parseFloat(T, "0."), 0, epsilon));
        try expect(approxEqAbs(T, try parseFloat(T, ".1"), 0.1, epsilon));
        try expect(approxEqAbs(T, try parseFloat(T, ".0"), 0, epsilon));
        try expect(approxEqAbs(T, try parseFloat(T, ".1e-1"), 0.01, epsilon));

        try expectError(error.InvalidCharacter, parseFloat(T, ".")); // At least one digit is required.
        try expectError(error.InvalidCharacter, parseFloat(T, ".e1")); // At least one digit is required.
        try expectError(error.InvalidCharacter, parseFloat(T, "0.e")); // At least one digit is required.

        try expect(approxEqAbs(T, try parseFloat(T, "123142.1"), 123142.1, epsilon));
        try expect(approxEqAbs(T, try parseFloat(T, "-123142.1124"), @as(T, -123142.1124), epsilon));
        try expect(approxEqAbs(T, try parseFloat(T, "0.7062146892655368"), @as(T, 0.7062146892655368), epsilon));
        try expect(approxEqAbs(T, try parseFloat(T, "2.71828182845904523536"), @as(T, 2.718281828459045), epsilon));
    }
}

Source

  pub fn parseFloat(comptime T: type, s: []const u8) ParseFloatError!T {
    if (@typeInfo(T) != .float) {
        @compileError("Cannot parse a float into a non-floating point type.");
    }

    if (s.len == 0) {
        return error.InvalidCharacter;
    }

    var i: usize = 0;
    const negative = s[i] == '-';
    if (s[i] == '-' or s[i] == '+') {
        i += 1;
    }
    if (s.len == i) {
        return error.InvalidCharacter;
    }

    const n = parse.parseNumber(T, s[i..], negative) orelse {
        return parse.parseInfOrNan(T, s[i..], negative) orelse error.InvalidCharacter;
    };

    if (n.hex) {
        return convertHex(T, n);
    }

    if (convertFast(T, n)) |f| {
        return f;
    }

    if (T == f16 or T == f32 or T == f64) {
        // If significant digits were truncated, then we can have rounding error
        // only if `mantissa + 1` produces a different result. We also avoid
        // redundantly using the Eisel-Lemire algorithm if it was unable to
        // correctly round on the first pass.
        if (convertEiselLemire(T, n.exponent, n.mantissa)) |bf| {
            if (!n.many_digits) {
                return bf.toFloat(T, n.negative);
            }
            if (convertEiselLemire(T, n.exponent, n.mantissa + 1)) |bf2| {
                if (bf.eql(bf2)) {
                    return bf.toFloat(T, n.negative);
                }
            }
        }
    }

    // Unable to correctly round the float using the Eisel-Lemire algorithm.
    // Fallback to a slower, but always correct algorithm.
    return convertSlow(T, s[i..]).toFloat(T, negative);
}  