1 files changed, 332 insertions, 0 deletions
diff --git a/src/strconv/atoi.go b/src/strconv/atoi.go
new file mode 100644
index 0000000..520d826
--- /dev/null
+++ b/src/strconv/atoi.go
@@ -0,0 +1,332 @@
+// 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 strconv
+
+import "errors"
+
+// lower(c) is a lower-case letter if and only if
+// c is either that lower-case letter or the equivalent upper-case letter.
+// Instead of writing c == 'x' || c == 'X' one can write lower(c) == 'x'.
+// Note that lower of non-letters can produce other non-letters.
+func lower(c byte) byte {
+	return c | ('x' - 'X')
+}
+
+// ErrRange indicates that a value is out of range for the target type.
+var ErrRange = errors.New("value out of range")
+
+// ErrSyntax indicates that a value does not have the right syntax for the target type.
+var ErrSyntax = errors.New("invalid syntax")
+
+// A NumError records a failed conversion.
+type NumError struct {
+	Func string // the failing function (ParseBool, ParseInt, ParseUint, ParseFloat, ParseComplex)
+	Num  string // the input
+	Err  error  // the reason the conversion failed (e.g. ErrRange, ErrSyntax, etc.)
+}
+
+func (e *NumError) Error() string {
+	return "strconv." + e.Func + ": " + "parsing " + Quote(e.Num) + ": " + e.Err.Error()
+}
+
+func (e *NumError) Unwrap() error { return e.Err }
+
+// cloneString returns a string copy of x.
+//
+// All ParseXXX functions allow the input string to escape to the error value.
+// This hurts strconv.ParseXXX(string(b)) calls where b is []byte since
+// the conversion from []byte must allocate a string on the heap.
+// If we assume errors are infrequent, then we can avoid escaping the input
+// back to the output by copying it first. This allows the compiler to call
+// strconv.ParseXXX without a heap allocation for most []byte to string
+// conversions, since it can now prove that the string cannot escape Parse.
+//
+// TODO: Use strings.Clone instead? However, we cannot depend on "strings"
+// since it incurs a transitive dependency on "unicode".
+// Either move strings.Clone to an internal/bytealg or make the
+// "strings" to "unicode" dependency lighter (see https://go.dev/issue/54098).
+func cloneString(x string) string { return string([]byte(x)) }
+
+func syntaxError(fn, str string) *NumError {
+	return &NumError{fn, cloneString(str), ErrSyntax}
+}
+
+func rangeError(fn, str string) *NumError {
+	return &NumError{fn, cloneString(str), ErrRange}
+}
+
+func baseError(fn, str string, base int) *NumError {
+	return &NumError{fn, cloneString(str), errors.New("invalid base " + Itoa(base))}
+}
+
+func bitSizeError(fn, str string, bitSize int) *NumError {
+	return &NumError{fn, cloneString(str), errors.New("invalid bit size " + Itoa(bitSize))}
+}
+
+const intSize = 32 << (^uint(0) >> 63)
+
+// IntSize is the size in bits of an int or uint value.
+const IntSize = intSize
+
+const maxUint64 = 1<<64 - 1
+
+// ParseUint is like ParseInt but for unsigned numbers.
+//
+// A sign prefix is not permitted.
+func ParseUint(s string, base int, bitSize int) (uint64, error) {
+	const fnParseUint = "ParseUint"
+
+	if s == "" {
+		return 0, syntaxError(fnParseUint, s)
+	}
+
+	base0 := base == 0
+
+	s0 := s
+	switch {
+	case 2 <= base && base <= 36:
+		// valid base; nothing to do
+
+	case base == 0:
+		// Look for octal, hex prefix.
+		base = 10
+		if s[0] == '0' {
+			switch {
+			case len(s) >= 3 && lower(s[1]) == 'b':
+				base = 2
+				s = s[2:]
+			case len(s) >= 3 && lower(s[1]) == 'o':
+				base = 8
+				s = s[2:]
+			case len(s) >= 3 && lower(s[1]) == 'x':
+				base = 16
+				s = s[2:]
+			default:
+				base = 8
+				s = s[1:]
+			}
+		}
+
+	default:
+		return 0, baseError(fnParseUint, s0, base)
+	}
+
+	if bitSize == 0 {
+		bitSize = IntSize
+	} else if bitSize < 0 || bitSize > 64 {
+		return 0, bitSizeError(fnParseUint, s0, bitSize)
+	}
+
+	// Cutoff is the smallest number such that cutoff*base > maxUint64.
+	// Use compile-time constants for common cases.
+	var cutoff uint64
+	switch base {
+	case 10:
+		cutoff = maxUint64/10 + 1
+	case 16:
+		cutoff = maxUint64/16 + 1
+	default:
+		cutoff = maxUint64/uint64(base) + 1
+	}
+
+	maxVal := uint64(1)<<uint(bitSize) - 1
+
+	underscores := false
+	var n uint64
+	for _, c := range []byte(s) {
+		var d byte
+		switch {
+		case c == '_' && base0:
+			underscores = true
+			continue
+		case '0' <= c && c <= '9':
+			d = c - '0'
+		case 'a' <= lower(c) && lower(c) <= 'z':
+			d = lower(c) - 'a' + 10
+		default:
+			return 0, syntaxError(fnParseUint, s0)
+		}
+
+		if d >= byte(base) {
+			return 0, syntaxError(fnParseUint, s0)
+		}
+
+		if n >= cutoff {
+			// n*base overflows
+			return maxVal, rangeError(fnParseUint, s0)
+		}
+		n *= uint64(base)
+
+		n1 := n + uint64(d)
+		if n1 < n || n1 > maxVal {
+			// n+d overflows
+			return maxVal, rangeError(fnParseUint, s0)
+		}
+		n = n1
+	}
+
+	if underscores && !underscoreOK(s0) {
+		return 0, syntaxError(fnParseUint, s0)
+	}
+
+	return n, nil
+}
+
+// ParseInt interprets a string s in the given base (0, 2 to 36) and
+// bit size (0 to 64) and returns the corresponding value i.
+//
+// The string may begin with a leading sign: "+" or "-".
+//
+// If the base argument is 0, the true base is implied by the string's
+// prefix following the sign (if present): 2 for "0b", 8 for "0" or "0o",
+// 16 for "0x", and 10 otherwise. Also, for argument base 0 only,
+// underscore characters are permitted as defined by the Go syntax for
+// [integer literals].
+//
+// The bitSize argument specifies the integer type
+// that the result must fit into. Bit sizes 0, 8, 16, 32, and 64
+// correspond to int, int8, int16, int32, and int64.
+// If bitSize is below 0 or above 64, an error is returned.
+//
+// The errors that ParseInt returns have concrete type *NumError
+// and include err.Num = s. If s is empty or contains invalid
+// digits, err.Err = ErrSyntax and the returned value is 0;
+// if the value corresponding to s cannot be represented by a
+// signed integer of the given size, err.Err = ErrRange and the
+// returned value is the maximum magnitude integer of the
+// appropriate bitSize and sign.
+//
+// [integer literals]: https://go.dev/ref/spec#Integer_literals
+func ParseInt(s string, base int, bitSize int) (i int64, err error) {
+	const fnParseInt = "ParseInt"
+
+	if s == "" {
+		return 0, syntaxError(fnParseInt, s)
+	}
+
+	// Pick off leading sign.
+	s0 := s
+	neg := false
+	if s[0] == '+' {
+		s = s[1:]
+	} else if s[0] == '-' {
+		neg = true
+		s = s[1:]
+	}
+
+	// Convert unsigned and check range.
+	var un uint64
+	un, err = ParseUint(s, base, bitSize)
+	if err != nil && err.(*NumError).Err != ErrRange {
+		err.(*NumError).Func = fnParseInt
+		err.(*NumError).Num = cloneString(s0)
+		return 0, err
+	}
+
+	if bitSize == 0 {
+		bitSize = IntSize
+	}
+
+	cutoff := uint64(1 << uint(bitSize-1))
+	if !neg && un >= cutoff {
+		return int64(cutoff - 1), rangeError(fnParseInt, s0)
+	}
+	if neg && un > cutoff {
+		return -int64(cutoff), rangeError(fnParseInt, s0)
+	}
+	n := int64(un)
+	if neg {
+		n = -n
+	}
+	return n, nil
+}
+
+// Atoi is equivalent to ParseInt(s, 10, 0), converted to type int.
+func Atoi(s string) (int, error) {
+	const fnAtoi = "Atoi"
+
+	sLen := len(s)
+	if intSize == 32 && (0 < sLen && sLen < 10) ||
+		intSize == 64 && (0 < sLen && sLen < 19) {
+		// Fast path for small integers that fit int type.
+		s0 := s
+		if s[0] == '-' || s[0] == '+' {
+			s = s[1:]
+			if len(s) < 1 {
+				return 0, syntaxError(fnAtoi, s0)
+			}
+		}
+
+		n := 0
+		for _, ch := range []byte(s) {
+			ch -= '0'
+			if ch > 9 {
+				return 0, syntaxError(fnAtoi, s0)
+			}
+			n = n*10 + int(ch)
+		}
+		if s0[0] == '-' {
+			n = -n
+		}
+		return n, nil
+	}
+
+	// Slow path for invalid, big, or underscored integers.
+	i64, err := ParseInt(s, 10, 0)
+	if nerr, ok := err.(*NumError); ok {
+		nerr.Func = fnAtoi
+	}
+	return int(i64), err
+}
+
+// underscoreOK reports whether the underscores in s are allowed.
+// Checking them in this one function lets all the parsers skip over them simply.
+// Underscore must appear only between digits or between a base prefix and a digit.
+func underscoreOK(s string) bool {
+	// saw tracks the last character (class) we saw:
+	// ^ for beginning of number,
+	// 0 for a digit or base prefix,
+	// _ for an underscore,
+	// ! for none of the above.
+	saw := '^'
+	i := 0
+
+	// Optional sign.
+	if len(s) >= 1 && (s[0] == '-' || s[0] == '+') {
+		s = s[1:]
+	}
+
+	// Optional base prefix.
+	hex := false
+	if len(s) >= 2 && s[0] == '0' && (lower(s[1]) == 'b' || lower(s[1]) == 'o' || lower(s[1]) == 'x') {
+		i = 2
+		saw = '0' // base prefix counts as a digit for "underscore as digit separator"
+		hex = lower(s[1]) == 'x'
+	}
+
+	// Number proper.
+	for ; i < len(s); i++ {
+		// Digits are always okay.
+		if '0' <= s[i] && s[i] <= '9' || hex && 'a' <= lower(s[i]) && lower(s[i]) <= 'f' {
+			saw = '0'
+			continue
+		}
+		// Underscore must follow digit.
+		if s[i] == '_' {
+			if saw != '0' {
+				return false
+			}
+			saw = '_'
+			continue
+		}
+		// Underscore must also be followed by digit.
+		if saw == '_' {
+			return false
+		}
+		// Saw non-digit, non-underscore.
+		saw = '!'
+	}
+	return saw != '_'
+}