}
func special(s string) (f float64, ok bool) {
- switch {
- case equalIgnoreCase(s, "nan"):
- return math.NaN(), true
- case equalIgnoreCase(s, "-inf"),
- equalIgnoreCase(s, "-infinity"):
- return math.Inf(-1), true
- case equalIgnoreCase(s, "+inf"),
- equalIgnoreCase(s, "+infinity"),
- equalIgnoreCase(s, "inf"),
- equalIgnoreCase(s, "infinity"):
- return math.Inf(1), true
+ if len(s) == 0 {
+ return
+ }
+ switch s[0] {
+ default:
+ return
+ case '+':
+ if equalIgnoreCase(s, "+inf") || equalIgnoreCase(s, "+infinity") {
+ return math.Inf(1), true
+ }
+ case '-':
+ if equalIgnoreCase(s, "-inf") || equalIgnoreCase(s, "-infinity") {
+ return math.Inf(-1), true
+ }
+ case 'n', 'N':
+ if equalIgnoreCase(s, "nan") {
+ return math.NaN(), true
+ }
+ case 'i', 'I':
+ if equalIgnoreCase(s, "inf") || equalIgnoreCase(s, "infinity") {
+ return math.Inf(1), true
+ }
}
return
}
return
}
+// readFloat reads a decimal mantissa and exponent from a float
+// string representation. It sets ok to false if the number could
+// not fit return types or is invalid.
+func readFloat(s string) (mantissa uint64, exp int, neg, trunc, ok bool) {
+ const uint64digits = 19
+ i := 0
+
+ // optional sign
+ if i >= len(s) {
+ return
+ }
+ switch {
+ case s[i] == '+':
+ i++
+ case s[i] == '-':
+ neg = true
+ i++
+ }
+
+ // digits
+ sawdot := false
+ sawdigits := false
+ nd := 0
+ ndMant := 0
+ dp := 0
+ for ; i < len(s); i++ {
+ switch c := s[i]; true {
+ case c == '.':
+ if sawdot {
+ return
+ }
+ sawdot = true
+ dp = nd
+ continue
+
+ case '0' <= c && c <= '9':
+ sawdigits = true
+ if c == '0' && nd == 0 { // ignore leading zeros
+ dp--
+ continue
+ }
+ nd++
+ if ndMant < uint64digits {
+ mantissa *= 10
+ mantissa += uint64(c - '0')
+ ndMant++
+ } else if s[i] != '0' {
+ trunc = true
+ }
+ continue
+ }
+ break
+ }
+ if !sawdigits {
+ return
+ }
+ if !sawdot {
+ dp = nd
+ }
+
+ // optional exponent moves decimal point.
+ // if we read a very large, very long number,
+ // just be sure to move the decimal point by
+ // a lot (say, 100000). it doesn't matter if it's
+ // not the exact number.
+ if i < len(s) && (s[i] == 'e' || s[i] == 'E') {
+ i++
+ if i >= len(s) {
+ return
+ }
+ esign := 1
+ if s[i] == '+' {
+ i++
+ } else if s[i] == '-' {
+ i++
+ esign = -1
+ }
+ if i >= len(s) || s[i] < '0' || s[i] > '9' {
+ return
+ }
+ e := 0
+ for ; i < len(s) && '0' <= s[i] && s[i] <= '9'; i++ {
+ if e < 10000 {
+ e = e*10 + int(s[i]) - '0'
+ }
+ }
+ dp += e * esign
+ }
+
+ if i != len(s) {
+ return
+ }
+
+ exp = dp - ndMant
+ ok = true
+ return
+
+}
+
// decimal power of ten to binary power of two.
var powtab = []int{1, 3, 6, 9, 13, 16, 19, 23, 26}
return bits, overflow
}
-// Compute exact floating-point integer from d's digits.
-// Caller is responsible for avoiding overflow.
-func (d *decimal) atof64int() float64 {
- f := 0.0
- for i := 0; i < d.nd; i++ {
- f = f*10 + float64(d.d[i]-'0')
- }
- if d.neg {
- f = -f
- }
- return f
-}
-
func (d *decimal) atof32int() float32 {
f := float32(0)
for i := 0; i < d.nd; i++ {
return f
}
-// Reads a uint64 decimal mantissa, which might be truncated.
-func (d *decimal) atou64() (mant uint64, digits int) {
- const uint64digits = 19
- for i, c := range d.d[:d.nd] {
- if i == uint64digits {
- return mant, i
- }
- mant = 10*mant + uint64(c-'0')
- }
- return mant, d.nd
-}
-
// Exact powers of 10.
var float64pow10 = []float64{
1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9,
}
var float32pow10 = []float32{1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9, 1e10}
-// If possible to convert decimal d to 64-bit float f exactly,
+// If possible to convert decimal representation to 64-bit float f exactly,
// entirely in floating-point math, do so, avoiding the expense of decimalToFloatBits.
// Three common cases:
// value is exact integer
// value is exact integer * exact power of ten
// value is exact integer / exact power of ten
// These all produce potentially inexact but correctly rounded answers.
-func (d *decimal) atof64() (f float64, ok bool) {
- // Exact integers are <= 10^15.
- // Exact powers of ten are <= 10^22.
- if d.nd > 15 {
+func atof64exact(mantissa uint64, exp int, neg bool) (f float64, ok bool) {
+ if mantissa>>float64info.mantbits != 0 {
return
}
+ f = float64(mantissa)
+ if neg {
+ f = -f
+ }
switch {
- case d.dp == d.nd: // int
- f := d.atof64int()
+ case exp == 0:
+ // an integer.
return f, true
-
- case d.dp > d.nd && d.dp <= 15+22: // int * 10^k
- f := d.atof64int()
- k := d.dp - d.nd
+ // Exact integers are <= 10^15.
+ // Exact powers of ten are <= 10^22.
+ case 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 k > 22 {
- f *= float64pow10[k-22]
- k = 22
+ if exp > 22 {
+ f *= float64pow10[exp-22]
+ exp = 22
}
- return f * float64pow10[k], true
-
- case d.dp < d.nd && d.nd-d.dp <= 22: // int / 10^k
- f := d.atof64int()
- return f / float64pow10[d.nd-d.dp], true
+ if f > 1e15 || f < -1e15 {
+ // the exponent was really too large.
+ return
+ }
+ return f * float64pow10[exp], true
+ case exp < 0 && exp >= -22: // int / 10^k
+ return f / float64pow10[-exp], true
}
return
}
return val, nil
}
- var d decimal
- if !d.set(s) {
- return 0, syntaxError(fnParseFloat, s)
- }
if optimize {
- if f, ok := d.atof64(); ok {
- return f, nil
- }
-
- // Try another fast path.
- ext := new(extFloat)
- if ok := ext.AssignDecimal(&d); ok {
- b, ovf := ext.floatBits()
- f = math.Float64frombits(b)
- if ovf {
- err = rangeError(fnParseFloat, s)
+ // Parse mantissa and exponent.
+ mantissa, exp, neg, trunc, ok := readFloat(s)
+ if ok {
+ // Try pure floating-point arithmetic conversion.
+ if !trunc {
+ if f, ok := atof64exact(mantissa, exp, neg); ok {
+ return f, nil
+ }
+ }
+ // Try another fast path.
+ ext := new(extFloat)
+ if ok := ext.AssignDecimal(mantissa, exp, neg, trunc); ok {
+ b, ovf := ext.floatBits()
+ f = math.Float64frombits(b)
+ if ovf {
+ err = rangeError(fnParseFloat, s)
+ }
+ return f, err
}
- return f, err
}
}
+ var d decimal
+ if !d.set(s) {
+ return 0, syntaxError(fnParseFloat, s)
+ }
b, ovf := d.floatBits(&float64info)
f = math.Float64frombits(b)
if ovf {