ryu-ecmascript 0.1.1

// Translated from C to Rust. The original C code can be found at
// https://github.com/ulfjack/ryu and carries the following license:
//
// Copyright 2018 Ulf Adams
//
// The contents of this file may be used under the terms of the Apache License,
// Version 2.0.
//
//    (See accompanying file LICENSE-Apache or copy at
//     http://www.apache.org/licenses/LICENSE-2.0)
//
// Alternatively, the contents of this file may be used under the terms of
// the Boost Software License, Version 1.0.
//    (See accompanying file LICENSE-Boost or copy at
//     https://www.boost.org/LICENSE_1_0.txt)
//
// Unless required by applicable law or agreed to in writing, this software
// is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.

use core::ptr;

// Returns e == 0 ? 1 : ceil(log_2(5^e)).
#[cfg_attr(feature = "no-panic", inline)]
pub fn pow5bits(e: i32) -> u32 {
    // This approximation works up to the point that the multiplication overflows at e = 3529.
    // If the multiplication were done in 64 bits, it would fail at 5^4004 which is just greater
    // than 2^9297.
    debug_assert!(e >= 0);
    debug_assert!(e <= 3528);
    ((e as u32 * 1217359) >> 19) + 1
}

// Returns floor(log_10(2^e)).
#[cfg_attr(feature = "no-panic", inline)]
pub fn log10_pow2(e: i32) -> i32 {
    // The first value this approximation fails for is 2^1651 which is just greater than 10^297.
    debug_assert!(e >= 0);
    debug_assert!(e <= 1650);
    ((e as u32 * 78913) >> 18) as i32
}

// Returns floor(log_10(5^e)).
#[cfg_attr(feature = "no-panic", inline)]
pub fn log10_pow5(e: i32) -> i32 {
    // The first value this approximation fails for is 5^2621 which is just greater than 10^1832.
    debug_assert!(e >= 0);
    debug_assert!(e <= 2620);
    ((e as u32 * 732923) >> 20) as i32
}

#[cfg_attr(feature = "no-panic", inline)]
pub unsafe fn copy_special_str(result: *mut u8,
                               sign: bool,
                               exponent: bool,
                               mantissa: bool)
                               -> usize {
    if mantissa {
        ptr::copy_nonoverlapping(b"NaN".as_ptr(), result, 3);
        return 3;
    }
    if sign {
        *result = b'-';
    }
    if exponent {
        ptr::copy_nonoverlapping(b"Infinity".as_ptr(), result.offset(sign as isize), 8);
        return sign as usize + 8;
    }
    ptr::copy_nonoverlapping(b"0E0".as_ptr(), result.offset(sign as isize), 3);
    sign as usize + 3
}