golang atoc 代码
文件路径：/src/strconv/atoc.go
/ 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
}