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float.go
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float.go
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// Copyright (c) 2015 Taco de Wolff
//
// Permission is hereby granted, free of charge, to any person
// obtaining a copy of this software and associated documentation
// files (the "Software"), to deal in the Software without
// restriction, including without limitation the rights to use,
// copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following
// conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
// OTHER DEALINGS IN THE SOFTWARE.
// This package contains string conversion function and is written in [Go][1].
// It is much alike the standard library's strconv package, but it is
// specifically tailored for the performance needs within the minify package.
// For example, the floating-point to string conversion function is
// approximately twice as fast as the standard library, but it is not as
// precise.
package byteconv
import (
"math"
"strconv"
)
var float64pow10 = []float64{
1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9,
1e10, 1e11, 1e12, 1e13, 1e14, 1e15, 1e16, 1e17, 1e18, 1e19,
1e20, 1e21, 1e22,
}
// Float parses a byte-slice and returns the float it represents.
// If an invalid character is encountered, it will stop there.
func ParseFloat(b []byte) (v float64, ok bool, err error) {
if len(b) == 0 {
return
}
if UseStdLib {
v, err = strconv.ParseFloat(string(b), 64)
ok = err == nil
return
}
i := 0
neg := false
if i < len(b) && (b[i] == '+' || b[i] == '-') {
neg = b[i] == '-'
i++
}
dot := -1
trunk := -1
n := uint64(0)
for ; i < len(b); i++ {
c := b[i]
if c >= '0' && c <= '9' {
if trunk == -1 {
if n > math.MaxUint64/10 {
trunk = i
} else {
n *= 10
n += uint64(c - '0')
}
}
} else if dot == -1 && c == '.' {
dot = i
} else {
if c == 'e' || c == 'E' {
break
}
return 0, false, syntaxError("ParseFloat", string(b))
}
}
f := float64(n)
if neg {
f = -f
}
mantExp := int64(0)
if dot != -1 {
if trunk == -1 {
trunk = i
}
mantExp = int64(trunk - dot - 1)
} else if trunk != -1 {
mantExp = int64(trunk - i)
}
expExp := int64(0)
if i < len(b) && (b[i] == 'e' || b[i] == 'E') {
i++
if e, ok, err := ParseInt(b[i:]); ok && err == nil {
expExp = e
i += LenInt(e)
} else {
return 0, false, syntaxError("ParseFloat", string(b))
}
}
exp := expExp - mantExp
// copied from strconv/atof.go
if exp == 0 {
return f, true, nil
} else if exp > 0 && exp <= 15+22 { // int * 10^k
// If exponent is big but number of digits is not,
// can move a few zeros into the integer part.
if exp > 22 {
f *= float64pow10[exp-22]
exp = 22
}
if f <= 1e15 && f >= -1e15 {
return f * float64pow10[exp], true, nil
}
} else if exp < 0 && exp >= -22 { // int / 10^k
return f / float64pow10[-exp], true, nil
}
f *= math.Pow10(int(-mantExp))
return f * math.Pow10(int(expExp)), true, nil
}