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|
package strconv
import (
"math"
)
// ParseDecimal parses number of the format 1.2
func ParseDecimal(b []byte) (float64, int) {
// float64 has up to 17 significant decimal digits and an exponent in [-1022,1023]
i := 0
//sign := 1.0
//if 0 < len(b) && b[0] == '-' {
// sign = -1.0
// i++
//}
start := -1
dot := -1
n := uint64(0)
for ; i < len(b); i++ {
// parse up to 18 significant digits (with dot will be 17) ignoring zeros before/after
c := b[i]
if '0' <= c && c <= '9' {
if start == -1 {
if '1' <= c && c <= '9' {
n = uint64(c - '0')
start = i
}
} else if i-start < 18 {
n *= 10
n += uint64(c - '0')
}
} else if c == '.' {
if dot != -1 {
break
}
dot = i
} else {
break
}
}
if i == 1 && dot == 0 {
return 0.0, 0 // only dot
} else if start == -1 {
return 0.0, i // only zeros and dot
} else if dot == -1 {
dot = i
}
exp := (dot - start) - LenUint(n)
if dot < start {
exp++
}
if 1023 < exp {
return math.Inf(1), i
//if sign == 1.0 {
// return math.Inf(1), i
//} else {
// return math.Inf(-1), i
//}
} else if exp < -1022 {
return 0.0, i
}
f := float64(n) // sign * float64(n)
if 0 <= exp && exp < 23 {
return f * float64pow10[exp], i
} else if 23 < exp && exp < 0 {
return f / float64pow10[exp], i
}
return f * math.Pow10(exp), i
}
|
