1 files changed, 105 insertions, 0 deletions
diff --git a/src/strconv/atoc.go b/src/strconv/atoc.go
new file mode 100644
index 0000000..85c7baf
--- /dev/null
+++ b/src/strconv/atoc.go
@@ -0,0 +1,105 @@
+// Copyright 2020 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
+
+const fnParseComplex = "ParseComplex"
+
+// convErr splits an error returned by parseFloatPrefix
+// into a syntax or range error for ParseComplex.
+func convErr(err error, s string) (syntax, range_ error) {
+	if x, ok := err.(*NumError); ok {
+		x.Func = fnParseComplex
+		x.Num = s
+		if x.Err == ErrRange {
+			return nil, x
+		}
+	}
+	return err, nil
+}
+
+// ParseComplex converts the string s to a complex number
+// with the precision specified by bitSize: 64 for complex64, or 128 for complex128.
+// When bitSize=64, the result still has type complex128, but it will be
+// convertible to complex64 without changing its value.
+//
+// The number represented by s must be of the form N, Ni, or N±Ni, where N stands
+// for a floating-point number as recognized by ParseFloat, and i is the imaginary
+// component. If the second N is unsigned, a + sign is required between the two components
+// as indicated by the ±. If the second N is NaN, only a + sign is accepted.
+// The form may be parenthesized and cannot contain any spaces.
+// The resulting complex number consists of the two components converted by ParseFloat.
+//
+// The errors that ParseComplex returns have concrete type *NumError
+// and include err.Num = s.
+//
+// If s is not syntactically well-formed, ParseComplex returns err.Err = ErrSyntax.
+//
+// If s is syntactically well-formed but either component is more than 1/2 ULP
+// away from the largest floating point number of the given component's size,
+// ParseComplex returns err.Err = ErrRange and c = ±Inf for the respective component.
+func ParseComplex(s string, bitSize int) (complex128, error) {
+	size := 64
+	if bitSize == 64 {
+		size = 32 // complex64 uses float32 parts
+	}
+
+	orig := s
+
+	// Remove parentheses, if any.
+	if len(s) >= 2 && s[0] == '(' && s[len(s)-1] == ')' {
+		s = s[1 : len(s)-1]
+	}
+
+	var pending error // pending range error, or nil
+
+	// Read real part (possibly imaginary part if followed by 'i').
+	re, n, err := parseFloatPrefix(s, size)
+	if err != nil {
+		err, pending = convErr(err, orig)
+		if err != nil {
+			return 0, err
+		}
+	}
+	s = s[n:]
+
+	// If we have nothing left, we're done.
+	if len(s) == 0 {
+		return complex(re, 0), pending
+	}
+
+	// Otherwise, look at the next character.
+	switch s[0] {
+	case '+':
+		// Consume the '+' to avoid an error if we have "+NaNi", but
+		// do this only if we don't have a "++" (don't hide that error).
+		if len(s) > 1 && s[1] != '+' {
+			s = s[1:]
+		}
+	case '-':
+		// ok
+	case 'i':
+		// If 'i' is the last character, we only have an imaginary part.
+		if len(s) == 1 {
+			return complex(0, re), pending
+		}
+		fallthrough
+	default:
+		return 0, syntaxError(fnParseComplex, orig)
+	}
+
+	// Read imaginary part.
+	im, n, err := parseFloatPrefix(s, size)
+	if err != nil {
+		err, pending = convErr(err, orig)
+		if err != nil {
+			return 0, err
+		}
+	}
+	s = s[n:]
+	if s != "i" {
+		return 0, syntaxError(fnParseComplex, orig)
+	}
+	return complex(re, im), pending
+}