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-rw-r--r--src/strconv/atof.go540
1 files changed, 540 insertions, 0 deletions
diff --git a/src/strconv/atof.go b/src/strconv/atof.go
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--- /dev/null
+++ b/src/strconv/atof.go
@@ -0,0 +1,540 @@
+// Copyright 2009 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 implements conversions to and from string representations
+// of basic data types.
+package strconv
+
+// decimal to binary floating point conversion.
+// Algorithm:
+// 1) Store input in multiprecision decimal.
+// 2) Multiply/divide decimal by powers of two until in range [0.5, 1)
+// 3) Multiply by 2^precision and round to get mantissa.
+
+import "math"
+
+var optimize = true // can change for testing
+
+func equalIgnoreCase(s1, s2 string) bool {
+ if len(s1) != len(s2) {
+ return false
+ }
+ for i := 0; i < len(s1); i++ {
+ c1 := s1[i]
+ if 'A' <= c1 && c1 <= 'Z' {
+ c1 += 'a' - 'A'
+ }
+ c2 := s2[i]
+ if 'A' <= c2 && c2 <= 'Z' {
+ c2 += 'a' - 'A'
+ }
+ if c1 != c2 {
+ return false
+ }
+ }
+ return true
+}
+
+func special(s string) (f float64, ok bool) {
+ 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
+}
+
+func (b *decimal) set(s string) (ok bool) {
+ i := 0
+ b.neg = false
+ b.trunc = false
+
+ // optional sign
+ if i >= len(s) {
+ return
+ }
+ switch {
+ case s[i] == '+':
+ i++
+ case s[i] == '-':
+ b.neg = true
+ i++
+ }
+
+ // digits
+ sawdot := false
+ sawdigits := false
+ for ; i < len(s); i++ {
+ switch {
+ case s[i] == '.':
+ if sawdot {
+ return
+ }
+ sawdot = true
+ b.dp = b.nd
+ continue
+
+ case '0' <= s[i] && s[i] <= '9':
+ sawdigits = true
+ if s[i] == '0' && b.nd == 0 { // ignore leading zeros
+ b.dp--
+ continue
+ }
+ if b.nd < len(b.d) {
+ b.d[b.nd] = s[i]
+ b.nd++
+ } else if s[i] != '0' {
+ b.trunc = true
+ }
+ continue
+ }
+ break
+ }
+ if !sawdigits {
+ return
+ }
+ if !sawdot {
+ b.dp = b.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'
+ }
+ }
+ b.dp += e * esign
+ }
+
+ if i != len(s) {
+ return
+ }
+
+ ok = true
+ 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}
+
+func (d *decimal) floatBits(flt *floatInfo) (b uint64, overflow bool) {
+ var exp int
+ var mant uint64
+
+ // Zero is always a special case.
+ if d.nd == 0 {
+ mant = 0
+ exp = flt.bias
+ goto out
+ }
+
+ // Obvious overflow/underflow.
+ // These bounds are for 64-bit floats.
+ // Will have to change if we want to support 80-bit floats in the future.
+ if d.dp > 310 {
+ goto overflow
+ }
+ if d.dp < -330 {
+ // zero
+ mant = 0
+ exp = flt.bias
+ goto out
+ }
+
+ // Scale by powers of two until in range [0.5, 1.0)
+ exp = 0
+ for d.dp > 0 {
+ var n int
+ if d.dp >= len(powtab) {
+ n = 27
+ } else {
+ n = powtab[d.dp]
+ }
+ d.Shift(-n)
+ exp += n
+ }
+ for d.dp < 0 || d.dp == 0 && d.d[0] < '5' {
+ var n int
+ if -d.dp >= len(powtab) {
+ n = 27
+ } else {
+ n = powtab[-d.dp]
+ }
+ d.Shift(n)
+ exp -= n
+ }
+
+ // Our range is [0.5,1) but floating point range is [1,2).
+ exp--
+
+ // Minimum representable exponent is flt.bias+1.
+ // If the exponent is smaller, move it up and
+ // adjust d accordingly.
+ if exp < flt.bias+1 {
+ n := flt.bias + 1 - exp
+ d.Shift(-n)
+ exp += n
+ }
+
+ if exp-flt.bias >= 1<<flt.expbits-1 {
+ goto overflow
+ }
+
+ // Extract 1+flt.mantbits bits.
+ d.Shift(int(1 + flt.mantbits))
+ mant = d.RoundedInteger()
+
+ // Rounding might have added a bit; shift down.
+ if mant == 2<<flt.mantbits {
+ mant >>= 1
+ exp++
+ if exp-flt.bias >= 1<<flt.expbits-1 {
+ goto overflow
+ }
+ }
+
+ // Denormalized?
+ if mant&(1<<flt.mantbits) == 0 {
+ exp = flt.bias
+ }
+ goto out
+
+overflow:
+ // ±Inf
+ mant = 0
+ exp = 1<<flt.expbits - 1 + flt.bias
+ overflow = true
+
+out:
+ // Assemble bits.
+ bits := mant & (uint64(1)<<flt.mantbits - 1)
+ bits |= uint64((exp-flt.bias)&(1<<flt.expbits-1)) << flt.mantbits
+ if d.neg {
+ bits |= 1 << flt.mantbits << flt.expbits
+ }
+ return bits, overflow
+}
+
+// Exact powers of 10.
+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,
+}
+var float32pow10 = []float32{1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9, 1e10}
+
+// 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 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 exp == 0:
+ // an integer.
+ return f, true
+ // 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 exp > 22 {
+ f *= float64pow10[exp-22]
+ exp = 22
+ }
+ 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
+}
+
+// If possible to compute mantissa*10^exp to 32-bit float f exactly,
+// entirely in floating-point math, do so, avoiding the machinery above.
+func atof32exact(mantissa uint64, exp int, neg bool) (f float32, ok bool) {
+ if mantissa>>float32info.mantbits != 0 {
+ return
+ }
+ f = float32(mantissa)
+ if neg {
+ f = -f
+ }
+ switch {
+ case exp == 0:
+ return f, true
+ // Exact integers are <= 10^7.
+ // Exact powers of ten are <= 10^10.
+ case exp > 0 && exp <= 7+10: // int * 10^k
+ // If exponent is big but number of digits is not,
+ // can move a few zeros into the integer part.
+ if exp > 10 {
+ f *= float32pow10[exp-10]
+ exp = 10
+ }
+ if f > 1e7 || f < -1e7 {
+ // the exponent was really too large.
+ return
+ }
+ return f * float32pow10[exp], true
+ case exp < 0 && exp >= -10: // int / 10^k
+ return f / float32pow10[-exp], true
+ }
+ return
+}
+
+const fnParseFloat = "ParseFloat"
+
+func atof32(s string) (f float32, err error) {
+ if val, ok := special(s); ok {
+ return float32(val), nil
+ }
+
+ if optimize {
+ // Parse mantissa and exponent.
+ mantissa, exp, neg, trunc, ok := readFloat(s)
+ if ok {
+ // Try pure floating-point arithmetic conversion.
+ if !trunc {
+ if f, ok := atof32exact(mantissa, exp, neg); ok {
+ return f, nil
+ }
+ }
+ // Try another fast path.
+ ext := new(extFloat)
+ if ok := ext.AssignDecimal(mantissa, exp, neg, trunc, &float32info); ok {
+ b, ovf := ext.floatBits(&float32info)
+ f = math.Float32frombits(uint32(b))
+ if ovf {
+ err = rangeError(fnParseFloat, s)
+ }
+ return f, err
+ }
+ }
+ }
+ var d decimal
+ if !d.set(s) {
+ return 0, syntaxError(fnParseFloat, s)
+ }
+ b, ovf := d.floatBits(&float32info)
+ f = math.Float32frombits(uint32(b))
+ if ovf {
+ err = rangeError(fnParseFloat, s)
+ }
+ return f, err
+}
+
+func atof64(s string) (f float64, err error) {
+ if val, ok := special(s); ok {
+ return val, nil
+ }
+
+ if optimize {
+ // 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, &float64info); ok {
+ b, ovf := ext.floatBits(&float64info)
+ f = math.Float64frombits(b)
+ if ovf {
+ err = rangeError(fnParseFloat, s)
+ }
+ 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 {
+ err = rangeError(fnParseFloat, s)
+ }
+ return f, err
+}
+
+// ParseFloat converts the string s to a floating-point number
+// with the precision specified by bitSize: 32 for float32, or 64 for float64.
+// When bitSize=32, the result still has type float64, but it will be
+// convertible to float32 without changing its value.
+//
+// If s is well-formed and near a valid floating point number,
+// ParseFloat returns the nearest floating point number rounded
+// using IEEE754 unbiased rounding.
+//
+// The errors that ParseFloat returns have concrete type *NumError
+// and include err.Num = s.
+//
+// If s is not syntactically well-formed, ParseFloat returns err.Err = ErrSyntax.
+//
+// If s is syntactically well-formed but is more than 1/2 ULP
+// away from the largest floating point number of the given size,
+// ParseFloat returns f = ±Inf, err.Err = ErrRange.
+func ParseFloat(s string, bitSize int) (f float64, err error) {
+ if bitSize == 32 {
+ f1, err1 := atof32(s)
+ return float64(f1), err1
+ }
+ f1, err1 := atof64(s)
+ return f1, err1
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-05-17 22:16:29 +0000