Function formatScientific [src]

Write a FloatDecimal to a buffer in scientific form. The buffer provided must be greater than min_buffer_size in length. If no precision is specified, this function will never return an error. If a precision is specified, up to 8 + precision bytes will be written to the buffer. An error will be returned if the content will not fit. It is recommended to bound decimal formatting with an exact precision.

Prototype

pub fn formatScientific(comptime T: type, buf: []u8, f_: FloatDecimal(T), precision: ?usize) FormatError![]const u8

Parameters

T: typebuf: []u8f_: FloatDecimal(T)precision: ?usize

Possible Errors

BufferTooSmall

Source

  pub fn formatScientific(comptime T: type, buf: []u8, f_: FloatDecimal(T), precision: ?usize) FormatError![]const u8 {
    std.debug.assert(buf.len >= min_buffer_size);
    var f = f_;

    if (f.exponent == special_exponent) {
        return copySpecialStr(buf, f);
    }

    if (precision) |prec| {
        f = round(T, f, .scientific, prec);
    }

    var output = f.mantissa;
    const olength = decimalLength(output);

    if (precision) |prec| {
        // fixed bound: sign(1) + leading_digit(1) + point(1) + exp_sign(1) + exp_max(4)
        const req_bytes = 8 + prec;
        if (buf.len < req_bytes) {
            return error.BufferTooSmall;
        }
    }

    // Step 5: Print the scientific representation
    var index: usize = 0;
    if (f.sign) {
        buf[index] = '-';
        index += 1;
    }

    // 1.12345
    writeDecimal(buf[index + 2 ..], &output, olength - 1);
    buf[index] = '0' + @as(u8, @intCast(output % 10));
    buf[index + 1] = '.';
    index += 2;
    const dp_index = index;
    if (olength > 1) index += olength - 1 else index -= 1;

    if (precision) |prec| {
        index += @intFromBool(olength == 1);
        if (prec > olength - 1) {
            const len = prec - (olength - 1);
            @memset(buf[index..][0..len], '0');
            index += len;
        } else {
            index = dp_index + prec - @intFromBool(prec == 0);
        }
    }

    // e100
    buf[index] = 'e';
    index += 1;
    var exp = f.exponent + @as(i32, @intCast(olength)) - 1;
    if (exp < 0) {
        buf[index] = '-';
        index += 1;
        exp = -exp;
    }
    var uexp: u32 = @intCast(exp);
    const elength = decimalLength(uexp);
    writeDecimal(buf[index..], &uexp, elength);
    index += elength;

    return buf[0..index];
}  