Imported Upstream version 1.4upstream/1.4

1 files changed, 540 insertions, 0 deletions

diff --git a/src/strconv/atof.go b/src/strconv/atof.go
new file mode 100644
index 000000000..286206481
--- /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
+}