encodejson.go

package compiler

import (
	"math/bits"
)

// From https://github.com/goccy/go-json/blob/master/internal/encoder/string.go
// Modified to avoid use of unsafe (perhaps at some small cost in performance).

var needEscape = [256]bool{
	'"':  true,
	'\\': true,
	0x00: true,
	0x01: true,
	0x02: true,
	0x03: true,
	0x04: true,
	0x05: true,
	0x06: true,
	0x07: true,
	0x08: true,
	0x09: true,
	0x0a: true,
	0x0b: true,
	0x0c: true,
	0x0d: true,
	0x0e: true,
	0x0f: true,
	0x10: true,
	0x11: true,
	0x12: true,
	0x13: true,
	0x14: true,
	0x15: true,
	0x16: true,
	0x17: true,
	0x18: true,
	0x19: true,
	0x1a: true,
	0x1b: true,
	0x1c: true,
	0x1d: true,
	0x1e: true,
	0x1f: true,
	/* 0x20 - 0xff */
}

var hex = "0123456789abcdef"

const (
	lsb = 0x0101010101010101
	msb = 0x8080808080808080
)

func appendJsonString(buf []byte, s string) []byte {
	valLen := len(s)
	if valLen == 0 {
		return append(buf, `""`...)
	}
	buf = append(buf, '"')
	var (
		i, j int
	)
	if valLen >= 8 {
		// Original code used this unsafe func, which we replace with some nasty string indexing.
		//chunks := stringToUint64Slice(s)

		nChunks := 0
		for i := 0; i < len(s); {
			nChunks++
			var n uint64 = uint64(s[i])
			i++
			n |= uint64(s[i]) << 8
			i++
			n |= uint64(s[i]) << 16
			i++
			n |= uint64(s[i]) << 24
			i++
			n |= uint64(s[i]) << 32
			i++
			n |= uint64(s[i]) << 48
			i++

			// combine masks before checking for the MSB of each byte. We include
			// `n` in the mask to check whether any of the *input* byte MSBs were
			// set (i.e. the byte was outside the ASCII range).
			mask := n | (n - (lsb * 0x20)) |
				((n ^ (lsb * '"')) - lsb) |
				((n ^ (lsb * '\\')) - lsb)
			if (mask & msb) != 0 {
				j = bits.TrailingZeros64(mask&msb) / 8
				goto ESCAPE_END
			}
		}
		valLen := len(s)
		for i := nChunks * 8; i < valLen; i++ {
			if needEscape[s[i]] {
				j = i
				goto ESCAPE_END
			}
		}
		return append(append(buf, s...), '"')
	}
ESCAPE_END:
	for j < valLen {
		c := s[j]

		if !needEscape[c] {
			// fast path: most of the time, printable ascii characters are used
			j++
			continue
		}

		switch c {
		case '\\', '"':
			buf = append(buf, s[i:j]...)
			buf = append(buf, '\\', c)
			i = j + 1
			j = j + 1
			continue

		case '\n':
			buf = append(buf, s[i:j]...)
			buf = append(buf, '\\', 'n')
			i = j + 1
			j = j + 1
			continue

		case '\r':
			buf = append(buf, s[i:j]...)
			buf = append(buf, '\\', 'r')
			i = j + 1
			j = j + 1
			continue

		case '\t':
			buf = append(buf, s[i:j]...)
			buf = append(buf, '\\', 't')
			i = j + 1
			j = j + 1
			continue

		case 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x0B, 0x0C, 0x0E, 0x0F, // 0x00-0x0F
			0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F: // 0x10-0x1F
			buf = append(buf, s[i:j]...)
			buf = append(buf, `\u00`...)
			buf = append(buf, hex[c>>4], hex[c&0xF])
			i = j + 1
			j = j + 1
			continue
		}
		j++
	}

	return append(append(buf, s[i:]...), '"')
}

func appendJsonPosInt(buf []byte, v int) []byte {
	start := len(buf)
	nd := 0
	for {
		buf = append(buf, byte(v%10)+'0')
		nd++
		v /= 10
		if v == 0 {
			break
		}
	}
	for i := 0; i < nd/2; i++ {
		pos1 := start + i
		pos2 := start + nd - i - 1
		tmp := buf[pos1]
		buf[pos1] = buf[pos2]
		buf[pos2] = tmp
	}
	return buf
}