net/parse.go

// The following is copied from Go 1.16 official implementation.

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package net

// Bigger than we need, not too big to worry about overflow
const big = 0xFFFFFF

// Decimal to integer.
// Returns number, characters consumed, success.
func dtoi(s string) (n int, i int, ok bool) {
	n = 0
	for i = 0; i < len(s) && '0' <= s[i] && s[i] <= '9'; i++ {
		n = n*10 + int(s[i]-'0')
		if n >= big {
			return big, i, false
		}
	}
	if i == 0 {
		return 0, 0, false
	}
	return n, i, true
}

// Hexadecimal to integer.
// Returns number, characters consumed, success.
func xtoi(s string) (n int, i int, ok bool) {
	n = 0
	for i = 0; i < len(s); i++ {
		if '0' <= s[i] && s[i] <= '9' {
			n *= 16
			n += int(s[i] - '0')
		} else if 'a' <= s[i] && s[i] <= 'f' {
			n *= 16
			n += int(s[i]-'a') + 10
		} else if 'A' <= s[i] && s[i] <= 'F' {
			n *= 16
			n += int(s[i]-'A') + 10
		} else {
			break
		}
		if n >= big {
			return 0, i, false
		}
	}
	if i == 0 {
		return 0, i, false
	}
	return n, i, true
}

// xtoi2 converts the next two hex digits of s into a byte.
// If s is longer than 2 bytes then the third byte must be e.
// If the first two bytes of s are not hex digits or the third byte
// does not match e, false is returned.
func xtoi2(s string, e byte) (byte, bool) {
	if len(s) > 2 && s[2] != e {
		return 0, false
	}
	n, ei, ok := xtoi(s[:2])
	return byte(n), ok && ei == 2
}

// Convert unsigned integer to decimal string.
func uitoa(val uint) string {
	if val == 0 { // avoid string allocation
		return "0"
	}
	var buf [20]byte // big enough for 64bit value base 10
	i := len(buf) - 1
	for val >= 10 {
		q := val / 10
		buf[i] = byte('0' + val - q*10)
		i--
		val = q
	}
	// val < 10
	buf[i] = byte('0' + val)
	return string(buf[i:])
}

// Convert i to a hexadecimal string. Leading zeros are not printed.
func appendHex(dst []byte, i uint32) []byte {
	if i == 0 {
		return append(dst, '0')
	}
	for j := 7; j >= 0; j-- {
		v := i >> uint(j*4)
		if v > 0 {
			dst = append(dst, hexDigit[v&0xf])
		}
	}
	return dst
}

// Index of rightmost occurrence of b in s.
func last(s string, b byte) int {
	i := len(s)
	for i--; i >= 0; i-- {
		if s[i] == b {
			break
		}
	}
	return i
}