hopp/tape/encode.go

package tape

import "io"
import "math"
import "bufio"

// Encodable is any type that can write itself to an encoder.
type Encodable interface {
	// Encode sends data to encoder. It returns the amount of bytes written,
	// and an error if the write stopped early.
	Encode(encoder *Encoder) (n int, err error)
}
	
// Encoder encodes data to an io.Writer.
type Encoder struct {
	bufio.Writer
}

// NewEncoder creates a new encoder that writes to writer.
func NewEncoder(writer io.Writer) *Encoder {
	encoder := &Encoder { }
	encoder.Reset(writer)
	return encoder
}

// WriteInt8 encodes an 8-bit signed integer to the output writer.
func (this *Encoder) WriteInt8(value int8) (n int, err error) {
	return this.WriteUint8(uint8(value))
}

// WriteUint8 encodes an 8-bit unsigned integer to the output writer.
func (this *Encoder) WriteUint8(value uint8) (n int, err error) {
	return this.Write([]byte { byte(value) })
}

// WriteInt16 encodes an 16-bit signed integer to the output writer.
func (this *Encoder) WriteInt16(value int16) (n int, err error) {
	return this.WriteUint16(uint16(value))
}

// WriteUint16 encodes an 16-bit unsigned integer to the output writer.
func (this *Encoder) WriteUint16(value uint16) (n int, err error) {
	return this.Write([]byte {
		byte(value >> 8),
		byte(value),
	})
}

// WriteInt32 encodes an 32-bit signed integer to the output writer.
func (this *Encoder) WriteInt32(value int32) (n int, err error) {
	return this.WriteUint32(uint32(value))
}

// WriteUint32 encodes an 32-bit unsigned integer to the output writer.
func (this *Encoder) WriteUint32(value uint32) (n int, err error) {
	return this.Write([]byte {
		byte(value >> 24),
		byte(value >> 16),
		byte(value >> 8),
		byte(value),
	})
}

// WriteInt64 encodes an 64-bit signed integer to the output writer.
func (this *Encoder) WriteInt64(value int64) (n int, err error) {
	return this.WriteUint64(uint64(value))
}

// WriteUint64 encodes an 64-bit unsigned integer to the output writer.
func (this *Encoder) WriteUint64(value uint64) (n int, err error) {
	return this.Write([]byte {
		byte(value >> 56),
		byte(value >> 48),
		byte(value >> 40),
		byte(value >> 32),
		byte(value >> 24),
		byte(value >> 16),
		byte(value >> 8),
		byte(value),
	})
}

// WriteIntN encodes an N-byte signed integer to the output writer.
func (this *Encoder) WriteIntN(value int64, bytes int) (n int, err error) {
	return this.WriteUintN(uint64(value), bytes)
}

// for Write/ReadUintN, increase buffers if go somehow gets support for over 64
// bit integers. we could also make an expanding int type in goutil to use here,
// or maybe there is one in the stdlib. keep the int64 versions as well though
// because its ergonomic.
	
// WriteUintN encodes an N-byte unsigned integer to the output writer.
func (this *Encoder) WriteUintN(value uint64, bytes int) (n int, err error) {
	// TODO: don't make multiple write calls (without allocating)
	buffer := [1]byte { }
	for bytesLeft := bytes; bytesLeft > 0; bytesLeft -- {
		buffer[0] = byte(value) >> ((bytesLeft - 1) * 8)
		nn, err := this.Write(buffer[:])
		n += nn; if err != nil { return n, err }
	}
	return n, nil
}

// WriteFloat16 encodes a 16-bit floating point value to the output writer.
func (this *Encoder) WriteFloat16(value float32) (n int, err error) {
	return this.WriteUint16(f32bitsToF16bits(math.Float32bits(value)))
}

// WriteFloat32 encodes a 32-bit floating point value to the output writer.
func (this *Encoder) WriteFloat32(value float32) (n int, err error) {
	return this.WriteUint32(math.Float32bits(value))
}

// WriteFloat64 encodes a 64-bit floating point value to the output writer.
func (this *Encoder) WriteFloat64(value float64) (n int, err error) {
	return this.WriteUint64(math.Float64bits(value))
}

// WriteTag encodes a [Tag] to the output writer.
func (this *Encoder) WriteTag(value Tag) (n int, err error) {
	return this.WriteUint8(uint8(value))
}

// f32bitsToF16bits returns uint16 (Float16 bits) converted from the specified float32.
// Conversion rounds to nearest integer with ties to even.
// Taken from https://github.com/x448/float16/blob/v0.8.4/float16
//
// MIT License
// 
// Copyright (c) 2019 Montgomery Edwards⁴⁴⁸ and Faye Amacker
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
func f32bitsToF16bits(u32 uint32) uint16 {
	// Translated from Rust to Go by Montgomery Edwards⁴⁴⁸ (github.com/x448).
	// All 4294967296 conversions with this were confirmed to be correct by x448.
	// Original Rust implementation is by Kathryn Long (github.com/starkat99) with MIT license.

	sign := u32 & 0x80000000
	exp := u32 & 0x7f800000
	coef := u32 & 0x007fffff

	if exp == 0x7f800000 {
		// NaN or Infinity
		nanBit := uint32(0)
		if coef != 0 {
			nanBit = uint32(0x0200)
		}
		return uint16((sign >> 16) | uint32(0x7c00) | nanBit | (coef >> 13))
	}

	halfSign := sign >> 16

	unbiasedExp := int32(exp>>23) - 127
	halfExp := unbiasedExp + 15

	if halfExp >= 0x1f {
		return uint16(halfSign | uint32(0x7c00))
	}

	if halfExp <= 0 {
		if 14-halfExp > 24 {
			return uint16(halfSign)
		}
		coef := coef | uint32(0x00800000)
		halfCoef := coef >> uint32(14-halfExp)
		roundBit := uint32(1) << uint32(13-halfExp)
		if (coef&roundBit) != 0 && (coef&(3*roundBit-1)) != 0 {
			halfCoef++
		}
		return uint16(halfSign | halfCoef)
	}

	uHalfExp := uint32(halfExp) << 10
	halfCoef := coef >> 13
	roundBit := uint32(0x00001000)
	if (coef&roundBit) != 0 && (coef&(3*roundBit-1)) != 0 {
		return uint16((halfSign | uHalfExp | halfCoef) + 1)
	}
	return uint16(halfSign | uHalfExp | halfCoef)
}