1 files changed, 372 insertions, 0 deletions
diff --git a/src/pkg/strconv/atof.go b/src/pkg/strconv/atof.go
new file mode 100644
index 000000000..c257b2a33
--- /dev/null
+++ b/src/pkg/strconv/atof.go
@@ -0,0 +1,372 @@
+// 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.
+
+// 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.
+
+// The strconv package implements conversions to and from
+// string representations of basic data types.
+package strconv
+
+import (
+	"math";
+	"os";
+	"strconv";
+)
+
+var optimize = true	// can change for testing
+
+// TODO(rsc): Better truncation handling.
+func stringToDecimal(s string) (neg bool, d *decimal, trunc bool, ok bool) {
+	i := 0;
+
+	// optional sign
+	if i >= len(s) {
+		return;
+	}
+	switch {
+	case s[i] == '+':
+		i++;
+	case s[i] == '-':
+		neg = true;
+		i++;
+	}
+
+	// digits
+	b := new(decimal);
+	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;
+			}
+			b.d[b.nd] = s[i];
+			b.nd++;
+			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' {
+		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;
+	}
+
+	d = b;
+	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 decimalToFloatBits(neg bool, d *decimal, trunc bool, 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.
+	mant = d.Shift(int(1+flt.mantbits)).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 neg {
+		bits |= 1<<flt.mantbits<<flt.expbits;
+	}
+	return bits, overflow;
+}
+
+// Compute exact floating-point integer from d's digits.
+// Caller is responsible for avoiding overflow.
+func decimalAtof64Int(neg bool, d *decimal) float64 {
+	f := float64(0);
+	for i := 0; i < d.nd; i++ {
+		f = f*10 + float64(d.d[i] - '0');
+	}
+	if neg {
+		f *= -1;	// BUG work around 6g f = -f.
+	}
+	return f;
+}
+
+func decimalAtof32Int(neg bool, d *decimal) float32 {
+	f := float32(0);
+	for i := 0; i < d.nd; i++ {
+		f = f*10 + float32(d.d[i] - '0');
+	}
+	if neg {
+		f *= -1;	// BUG work around 6g f = -f.
+	}
+	return f;
+}
+
+// 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 d 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 decimalAtof64(neg bool, d *decimal, trunc bool) (f float64, ok bool) {
+	// Exact integers are <= 10^15.
+	// Exact powers of ten are <= 10^22.
+	if d.nd > 15 {
+		return;
+	}
+	switch {
+	case d.dp == d.nd:	// int
+		f := decimalAtof64Int(neg, d);
+		return f, true;
+
+	case d.dp > d.nd && d.dp <= 15+22:	// int * 10^k
+		f := decimalAtof64Int(neg, d);
+		k := d.dp - d.nd;
+		// 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;
+		}
+		return f*float64pow10[k], true;
+
+	case d.dp < d.nd && d.nd - d.dp <= 22:	// int / 10^k
+		f := decimalAtof64Int(neg, d);
+		return f/float64pow10[d.nd - d.dp], true;
+	}
+	return;
+}
+
+// If possible to convert decimal d to 32-bit float f exactly,
+// entirely in floating-point math, do so, avoiding the machinery above.
+func decimalAtof32(neg bool, d *decimal, trunc bool) (f float32, ok bool) {
+	// Exact integers are <= 10^7.
+	// Exact powers of ten are <= 10^10.
+	if d.nd > 7 {
+		return;
+	}
+	switch {
+	case d.dp == d.nd:	// int
+		f := decimalAtof32Int(neg, d);
+		return f, true;
+
+	case d.dp > d.nd && d.dp <= 7+10:	// int * 10^k
+		f := decimalAtof32Int(neg, d);
+		k := d.dp - d.nd;
+		// If exponent is big but number of digits is not,
+		// can move a few zeros into the integer part.
+		if k > 10 {
+			f *= float32pow10[k-10];
+			k = 10;
+		}
+		return f*float32pow10[k], true;
+
+	case d.dp < d.nd && d.nd - d.dp <= 10:	// int / 10^k
+		f := decimalAtof32Int(neg, d);
+		return f/float32pow10[d.nd - d.dp], true;
+	}
+	return;
+}
+
+// Atof32 converts the string s to a 32-bit floating-point number.
+//
+// If s is well-formed and near a valid floating point number,
+// Atof32 returns the nearest floating point number rounded
+// using IEEE754 unbiased rounding.
+//
+// If s is not syntactically well-formed, Atof32 returns err = os.EINVAL.
+//
+// If s is syntactically well-formed but is more than 1/2 ULP
+// away from the largest floating point number of the given size,
+// Atof32 returns f = ±Inf, err = os.ERANGE.
+func Atof32(s string) (f float32, err os.Error) {
+	neg, d, trunc, ok := stringToDecimal(s);
+	if !ok {
+		return 0, os.EINVAL;
+	}
+	if optimize {
+		if f, ok := decimalAtof32(neg, d, trunc); ok {
+			return f, nil;
+		}
+	}
+	b, ovf := decimalToFloatBits(neg, d, trunc, &float32info);
+	f = math.Float32frombits(uint32(b));
+	if ovf {
+		err = os.ERANGE;
+	}
+	return f, err
+}
+
+// Atof64 converts the string s to a 64-bit floating-point number.
+// Except for the type of its result, its definition is the same as that
+// of Atof32.
+func Atof64(s string) (f float64, err os.Error) {
+	neg, d, trunc, ok := stringToDecimal(s);
+	if !ok {
+		return 0, os.EINVAL;
+	}
+	if optimize {
+		if f, ok := decimalAtof64(neg, d, trunc); ok {
+			return f, nil;
+		}
+	}
+	b, ovf := decimalToFloatBits(neg, d, trunc, &float64info);
+	f = math.Float64frombits(b);
+	if ovf {
+		err = os.ERANGE;
+	}
+	return f, err
+}
+
+// Atof is like Atof32 or Atof64, depending on the size of float.
+func Atof(s string) (f float, err os.Error) {
+	if FloatSize == 32 {
+		f1, err1 := Atof32(s);
+		return float(f1), err1;
+	}
+	f1, err1 := Atof64(s);
+	return float(f1), err1;
+}
+