ryu-ecmascript 0.1.1

mod exponent;
mod mantissa;

use core::{mem, ptr};

use self::exponent::*;
use self::mantissa::*;
use d2s;
use d2s::*;
use f2s;
use f2s::*;

#[cfg(feature = "no-panic")]
use no_panic::no_panic;

#[cfg_attr(must_use_return, must_use)]
#[cfg_attr(feature = "no-panic", no_panic)]
pub unsafe fn d2s_buffered_n(f: f64, result: *mut u8) -> usize {
    let bits = mem::transmute::<f64, u64>(f);
    let sign = ((bits >> (DOUBLE_MANTISSA_BITS + DOUBLE_EXPONENT_BITS)) & 1) != 0;
    let ieee_mantissa = bits & ((1u64 << DOUBLE_MANTISSA_BITS) - 1);
    let ieee_exponent = (bits >> DOUBLE_MANTISSA_BITS) as u32 &
                        ((1u32 << DOUBLE_EXPONENT_BITS) - 1);

    let mut index = 0isize;
    if sign {
        *result = b'-';
        index += 1;
    }

    if ieee_exponent == 0 && ieee_mantissa == 0 {
        ptr::copy_nonoverlapping(b"0".as_ptr(), result.offset(index), 1);
        return sign as usize + 1;
    }

    let v = d2d(ieee_mantissa, ieee_exponent);

    let length = d2s::decimal_length(v.mantissa) as isize;
    let k = v.exponent as isize;
    let kk = length + k; // 10^(kk-1) <= v < 10^kk
    debug_assert!(k >= -324);

    // Mapping between ryu (left) and ECMAScript (right)
    // v.mantissa <=> s
    // length <=> k
    // k <=> n - k
    // kk <=> n

    if length <= kk && kk <= 21 {
        // 1234e7 -> 12340000000
        write_mantissa_long(v.mantissa, result.offset(index + length));
        for i in length..kk {
            *result.offset(index + i) = b'0';
        }
        index as usize + kk as usize
    } else if 0 < kk && kk <= 21 {
        // 1234e-2 -> 12.34
        write_mantissa_long(v.mantissa, result.offset(index + length + 1));
        ptr::copy(result.offset(index + 1), result.offset(index), kk as usize);
        *result.offset(index + kk) = b'.';
        index as usize + length as usize + 1
    } else if -6 < kk && kk <= 0 {
        // 1234e-6 -> 0.001234
        *result.offset(index) = b'0';
        *result.offset(index + 1) = b'.';
        let offset = 2 - kk;
        for i in 2..offset {
            *result.offset(index + i) = b'0';
        }
        write_mantissa_long(v.mantissa, result.offset(index + length + offset));
        index as usize + length as usize + offset as usize
    } else if length == 1 {
        // 1e+30
        *result.offset(index) = b'0' + v.mantissa as u8;
        *result.offset(index + 1) = b'e';
        index as usize + 2 + write_exponent3(kk - 1, result.offset(index + 2))
    } else {
        // 1234e30 -> 1.234e+33
        write_mantissa_long(v.mantissa, result.offset(index + length + 1));
        *result.offset(index) = *result.offset(index + 1);
        *result.offset(index + 1) = b'.';
        *result.offset(index + length + 1) = b'e';
        index as usize + length as usize + 2 +
        write_exponent3(kk - 1, result.offset(index + length + 2))
    }
}

#[cfg_attr(must_use_return, must_use)]
#[cfg_attr(feature = "no-panic", no_panic)]
pub unsafe fn f2s_buffered_n(f: f32, result: *mut u8) -> usize {
    let bits = mem::transmute::<f32, u32>(f);
    let sign = ((bits >> (FLOAT_MANTISSA_BITS + FLOAT_EXPONENT_BITS)) & 1) != 0;
    let ieee_mantissa = bits & ((1u32 << FLOAT_MANTISSA_BITS) - 1);
    let ieee_exponent = ((bits >> FLOAT_MANTISSA_BITS) & ((1u32 << FLOAT_EXPONENT_BITS) - 1)) as
                        u32;

    let mut index = 0isize;
    if sign {
        *result = b'-';
        index += 1;
    }

    if ieee_exponent == 0 && ieee_mantissa == 0 {
        ptr::copy_nonoverlapping(b"0".as_ptr(), result.offset(index), 1);
        return sign as usize + 1;
    }

    let v = f2d(ieee_mantissa, ieee_exponent);

    let length = f2s::decimal_length(v.mantissa) as isize;
    let k = v.exponent as isize;
    let kk = length + k; // 10^(kk-1) <= v < 10^kk
    debug_assert!(k >= -45);

    // Mapping between ryu (left) and ECMAScript (right)
    // v.mantissa <=> s
    // length <=> k
    // k <=> n - k
    // kk <=> n

    if length <= kk && kk <= 21 {
        // 1234e7 -> 12340000000
        write_mantissa(v.mantissa, result.offset(index + length));
        for i in length..kk {
            *result.offset(index + i) = b'0';
        }
        *result.offset(index + kk) = b'.';
        *result.offset(index + kk + 1) = b'0';
        index as usize + kk as usize + 2
    } else if 0 < kk && kk <= 21 {
        // 1234e-2 -> 12.34
        write_mantissa(v.mantissa, result.offset(index + length + 1));
        ptr::copy(result.offset(index + 1), result.offset(index), kk as usize);
        *result.offset(index + kk) = b'.';
        index as usize + length as usize + 1
    } else if -6 < kk && kk <= 0 {
        // 1234e-6 -> 0.001234
        *result.offset(index) = b'0';
        *result.offset(index + 1) = b'.';
        let offset = 2 - kk;
        for i in 2..offset {
            *result.offset(index + i) = b'0';
        }
        write_mantissa(v.mantissa, result.offset(index + length + offset));
        index as usize + length as usize + offset as usize
    } else if length == 1 {
        // 1e+30
        *result.offset(index) = b'0' + v.mantissa as u8;
        *result.offset(index + 1) = b'e';
        index as usize + 2 + write_exponent2(kk - 1, result.offset(index + 2))
    } else {
        // 1234e30 -> 1.234e+33
        write_mantissa(v.mantissa, result.offset(index + length + 1));
        *result.offset(index) = *result.offset(index + 1);
        *result.offset(index + 1) = b'.';
        *result.offset(index + length + 1) = b'e';
        index as usize + length as usize + 2 +
        write_exponent2(kk - 1, result.offset(index + length + 2))
    }
}