1 files changed, 220 insertions, 0 deletions
diff --git a/src/lib/strconv/atof.go b/src/lib/strconv/atof.go
new file mode 100644
index 000000000..2a34e8d07
--- /dev/null
+++ b/src/lib/strconv/atof.go
@@ -0,0 +1,220 @@
+// 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.
+
+package strconv
+
+import "strconv"
+
+// TODO(rsc): Better truncation handling, check for overflow in exponent.
+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 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++ {
+			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) {
+	// Zero is always a special case.
+	if d.nd == 0 {
+		return 0, false
+	}
+
+	// TODO: check for obvious overflow
+
+	// 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;
+	}
+
+	// TODO: overflow/underflow
+
+	// Extract 1+flt.mantbits bits.
+	mant := d.Shift(int(1+flt.mantbits)).RoundedInteger();
+
+	// Denormalized?
+	if mant&(1<<flt.mantbits) == 0 {
+		if exp != flt.bias+1 {
+			// TODO: remove - has no business panicking
+			panicln("DecimalToFloatBits", exp, flt.bias+1);
+		}
+		exp--;
+	} else {
+		if exp <= flt.bias {
+			// TODO: remove - has no business panicking
+			panicln("DecimalToFloatBits1", exp, flt.bias);
+		}
+	}
+
+	// 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, false;
+}
+
+// If possible to convert decimal d to 64-bit float f exactly,
+// entirely in floating-point math, do so, avoiding the machinery above.
+func DecimalToFloat64(neg bool, d *Decimal, trunc bool) (f float64, ok bool) {
+	// TODO: Fill in.
+	return 0, false;
+}
+
+// If possible to convert decimal d to 32-bit float f exactly,
+// entirely in floating-point math, do so, avoiding the machinery above.
+func DecimalToFloat32(neg bool, d *Decimal, trunc bool) (f float32, ok bool) {
+	// TODO: Fill in.
+	return 0, false;
+}
+
+export func atof64(s string) (f float64, overflow bool, ok bool) {
+	neg, d, trunc, ok1 := StringToDecimal(s);
+	if !ok1 {
+		return 0, false, false;
+	}
+	if f, ok := DecimalToFloat64(neg, d, trunc); ok {
+		return f, false, true;
+	}
+	b, overflow1 := DecimalToFloatBits(neg, d, trunc, &float64info);
+	return sys.float64frombits(b), overflow1, true;
+}
+
+export func atof32(s string) (f float32, overflow bool, ok bool) {
+	neg, d, trunc, ok1 := StringToDecimal(s);
+	if !ok1 {
+		return 0, false, false;
+	}
+	if f, ok := DecimalToFloat32(neg, d, trunc); ok {
+		return f, false, true;
+	}
+	b, overflow1 := DecimalToFloatBits(neg, d, trunc, &float32info);
+	return sys.float32frombits(uint32(b)), overflow1, true;
+}
+
+export func atof(s string) (f float, overflow bool, ok bool) {
+	if floatsize == 32 {
+		var f1 float32;
+		f1, overflow, ok = atof32(s);
+		return float(f1), overflow, ok;
+	}
+	var f1 float64;
+	f1, overflow, ok = atof64(s);
+	return float(f1), overflow, ok;
+}
+