klamath-rs/src/basic.rs

/*
 * Functionality for parsing and writing basic data types
 */
use nom;
use nom::{IResult};
use byteorder::BigEndian;
//use std::io::Write;
use std::io;


pub type OWResult = Result<usize, io::Error>;

/*
 * Parse functions
 */
//pub fn parse_byte_as_bits(input: &[u8]) -> IResult<&[u8], (u8, u8, u8, u8, u8, u8, u8, u8)> {
//    nom::bits::bits(nom::sequence::tuple((
//        nom::bits::complete::take::<_, _, _, CustomError<_>>(1_usize),
//        nom::bits::complete::take::<_, _, _, CustomError<_>>(1_usize),
//        nom::bits::complete::take::<_, _, _, CustomError<_>>(1_usize),
//        nom::bits::complete::take::<_, _, _, CustomError<_>>(1_usize),
//        nom::bits::complete::take::<_, _, _, CustomError<_>>(1_usize),
//        nom::bits::complete::take::<_, _, _, CustomError<_>>(1_usize),
//        nom::bits::complete::take::<_, _, _, CustomError<_>>(1_usize),
//        nom::bits::complete::take::<_, _, _, CustomError<_>>(1_usize),
//    )))(input)
//}


pub fn parse_int2(input: &[u8]) -> IResult<&[u8], i16> {
    nom::number::streaming::be_i16(input)?
}

pub fn parse_int4(input: &[u8]) -> IResult<&[u8], i32> {
    nom::number::streaming::be_i32(input)?
}

pub fn decode_real8(int: u64) -> f64 {
    // Convert GDS REAL8 to IEEE float64
    let neg = int & 0x8000_0000_0000_0000;
    let exp = (int >> 56) & 0x7f;
    let mut mant = (int & 0x00ff_ffff_ffff_ffff) as f64;
    if neg != 0 {
        mant *= -1
    }
    mant * 2_f64.powi(4 * (exp - 64) - 56)
}

pub fn parse_real8(input: &[u8]) -> IResult<&[u8], f64> {
    let data = nom::number::streaming::be_u64(input)?;
    IResult::Ok(decode_real8(data))
}


pub fn parse_datetime(input: &[u8]) -> IResult<&[u8], [u16; 6]> {
    let mut buf = [0_u16; 6];
    let mut parts = nom::multi::fill(parse_int2, &mut buf)(input);
    parts[0] += 1900;   // Year is from 1900
    IResult::Ok(parts)
}


pub fn parse_bitarray(input: &[u8]) -> IResult<&[u8], [bool; 16]> {
    let bits = [false; 16];
    let (input, val) = parse_int2(input)?;
    for ii in 0..16 {
        bits[ii] = ((val >> (16 - 1 - ii)) & 0x01) == 1;
    }
    bits
}


pub fn parse_ascii(input: &[u8], length: usize) -> IResult<&[u8], Vec<u8>> {
    let last = input[length - 1];
    let true_length = if last == '\0' { length - 1 } else { length };
    let vec = input[..true_length].to_vec();
    IResult::Ok((input[length..], vec))
}


/*
 * Pack functions
 */

pub fn pack_bitarray(bits: &[bool; 16]) -> u16 {
    let mut int: u16 = 0;
    for ii in 0..16 {
        int |= (bits[ii] as u16) << (16 - 1 - ii);
    }
    int
}


pub fn pack_int2(buf: &mut [u8], int: i16) {
    BigEndian::write_i16(&mut buf, int)
}

pub fn pack_int4(buf: &mut [u8], int: i32) {
    BigEndian::write_i32(&mut buf, int)
}

pub fn pack_real8(buf: &mut [u8], fnum: f64) {
    BigEndian::write_u64(&mut buf, encode_real8(fnum))
}

pub fn pack_ascii(buf: &mut [u8], data: &[u8]) -> usize {
    let len = data.len();
    buf[..len].copy_from_slice(data);
    if len % 2 == 1 {
        buf[len] = '\0';
        len + 1
    } else {
        len
    }
}


pub fn pack_datetime(buf: &mut [u8], date: &[u16; 6]) {
    assert!(buf.len() >= 6 * 2);
    let year = date[0] - 1900;
    pack_int2(&mut buf, year);
    for ii in 1..6 {
        pack_int2(&mut buf[(2 * ii)..], date[ii]);
    }
}


pub fn encode_real8(fnum: f64) -> u64 {
    // Convert from float64 to GDS REAL8 representation.

    // Split the ieee float bitfields
    let ieee = fnum.to_bits();
    let sign = ieee & 0x8000_0000_0000_0000;
    let ieee_exp = (ieee >> 52) as i32 & 0x7ff;
    let ieee_mant = ieee & 0xf_ffff_ffff_ffff;

    let subnorm = (ieee_exp == 0) & (ieee_mant != 0);
    if (ieee_exp == 0) & (ieee_mant == 0) {
        return 0
    }

    // IEEE normal double is (1 + ieee_mant / 2^52) * 2^(ieee_exp - 1023)
    // IEEE subnormal double is (ieee_mant / 2^52) * 2^(-1022)
    // GDS real8 is (gds_mant / 2^(7*8)) * 16^(gds_exp - 64)
    //            = (gds_mant / 2^56) * 2^(4 * gds_exp - 256)

    // Convert exponent.
    let exp2 = if subnorm { -1022 } else {ieee_exp + 1 - 1023};  // +1 is due to mantissa (1.xxxx in IEEE vs 0.xxxxx in GDSII)
    let mut exp16 = exp2 / 4;
    let rest = exp2 % 4;

    // Compensate for exponent coarseness
    let comp = rest != 0;
    let mut shift;
    if comp {
        exp16 += 1;
        shift = 4 - rest;
    } else {
        shift = rest;
    }
    shift -= 3;      // account for gds bit position

    // add leading one
    let mut gds_mant_unshifted = ieee_mant;
    if !subnorm {
        gds_mant_unshifted += 0x10_0000_0000_0000;
    }

    let mut gds_mant = if shift > 0 {
        gds_mant_unshifted >> shift
    } else {
        gds_mant_unshifted << -shift
    };

    // add gds exponent bias
    let mut gds_exp = exp16 + 64;

    if gds_exp < -14 {
        // number is too small
        return 0
    }

    let neg_biased = gds_exp < 0;
    if neg_biased {
        gds_mant >>= gds_exp * 4;
        gds_exp = 0;
    }

    let too_big = (gds_exp > 0x7f) & !subnorm;
    if too_big {
        panic!("Number too big for real8 format");       //TODO error handling
    }

    let gds_exp_bits = gds_exp << 56;

    let real8 = sign | gds_exp_bits | gds_mant;
    real8
}