math/big: incorporated feedback from prior TBR reviews
Change-Id: Ida847365223ef09b4a3846e240b4bb6919cb0fe9
Reviewed-on: https://go-review.googlesource.com/5610
Reviewed-by: Alan Donovan <adonovan@google.com>
diff --git a/src/math/big/float.go b/src/math/big/float.go
index 877379c..47755f2 100644
--- a/src/math/big/float.go
+++ b/src/math/big/float.go
@@ -39,10 +39,10 @@
// and according to its rounding mode, unless specified otherwise. If the
// result precision is 0 (see below), it is set to the precision of the
// argument with the largest precision value before any rounding takes
-// place. The rounding mode remains unchanged, thus uninitialized Floats
-// provided as result arguments will "inherit" a reasonble precision from
-// the incoming arguments and their mode is the zero value for RoundingMode
-// (ToNearestEven).
+// place, and the rounding mode remains unchanged. Thus, uninitialized Floats
+// provided as result arguments will have their precision set to a reasonable
+// value determined by the operands and their mode is the zero value for
+// RoundingMode (ToNearestEven).
//
// By setting the desired precision to 24 or 53 and using ToNearestEven
// rounding, Float operations produce the same results as the corresponding
@@ -62,6 +62,9 @@
prec uint // TODO(gri) make this a 32bit field
}
+// TODO(gri) provide a couple of Example tests showing typical Float intialization
+// and use.
+
// Internal representation: The mantissa bits x.mant of a Float x are stored
// in a nat slice long enough to hold up to x.prec bits; the slice may (but
// doesn't have to) be shorter if the mantissa contains trailing 0 bits.
@@ -158,7 +161,7 @@
// SetMode sets z's rounding mode to mode and returns an exact z.
// z remains unchanged otherwise.
func (z *Float) SetMode(mode RoundingMode) *Float {
- z.acc = Exact
+ z.acc = Exact // TODO(gri) should we not do this? what's the general rule for setting accuracy?
z.mode = mode
return z
}
@@ -274,23 +277,21 @@
}
// debugging support
-func validate(args ...*Float) {
- for i, x := range args {
- const msb = 1 << (_W - 1)
- m := len(x.mant)
- if m == 0 {
- // 0.0 or Inf
- if x.exp != 0 && x.exp != infExp {
- panic(fmt.Sprintf("#%d: %empty matissa with invalid exponent %d", i, x.exp))
- }
- continue
+func validate(x *Float) {
+ const msb = 1 << (_W - 1)
+ m := len(x.mant)
+ if m == 0 {
+ // 0.0 or Inf
+ if x.exp != 0 && x.exp != infExp {
+ panic(fmt.Sprintf("%empty matissa with invalid exponent %d", x.exp))
}
- if x.mant[m-1]&msb == 0 {
- panic(fmt.Sprintf("#%d: msb not set in last word %#x of %s", i, x.mant[m-1], x.Format('p', 0)))
- }
- if x.prec <= 0 {
- panic(fmt.Sprintf("#%d: invalid precision %d", i, x.prec))
- }
+ return
+ }
+ if x.mant[m-1]&msb == 0 {
+ panic(fmt.Sprintf("msb not set in last word %#x of %s", x.mant[m-1], x.Format('p', 0)))
+ }
+ if x.prec <= 0 {
+ panic(fmt.Sprintf("invalid precision %d", x.prec))
}
}
@@ -1064,7 +1065,8 @@
// result.
func (z *Float) Add(x, y *Float) *Float {
if debugFloat {
- validate(x, y)
+ validate(x)
+ validate(y)
}
if z.prec == 0 {
@@ -1104,7 +1106,8 @@
// Precision, rounding, and accuracy reporting are as for Add.
func (z *Float) Sub(x, y *Float) *Float {
if debugFloat {
- validate(x, y)
+ validate(x)
+ validate(y)
}
if z.prec == 0 {
@@ -1143,7 +1146,8 @@
// Precision, rounding, and accuracy reporting are as for Add.
func (z *Float) Mul(x, y *Float) *Float {
if debugFloat {
- validate(x, y)
+ validate(x)
+ validate(y)
}
if z.prec == 0 {
@@ -1171,7 +1175,8 @@
// Precision, rounding, and accuracy reporting are as for Add.
func (z *Float) Quo(x, y *Float) *Float {
if debugFloat {
- validate(x, y)
+ validate(x)
+ validate(y)
}
if z.prec == 0 {
@@ -1251,7 +1256,8 @@
// Infinities with matching sign are equal.
func (x *Float) Cmp(y *Float) int {
if debugFloat {
- validate(x, y)
+ validate(x)
+ validate(y)
}
mx := x.ord()
diff --git a/src/math/big/float_test.go b/src/math/big/float_test.go
index 17247b1..2789cfb 100644
--- a/src/math/big/float_test.go
+++ b/src/math/big/float_test.go
@@ -1077,6 +1077,8 @@
}
}
+// TODO(gri) Add tests that check correctness in the presence of aliasing.
+
// For rounding modes ToNegativeInf and ToPositiveInf, rounding is affected
// by the sign of the value to be rounded. Test that rounding happens after
// the sign of a result has been set.
diff --git a/src/math/big/int.go b/src/math/big/int.go
index 5c1b2cd..0695d78 100644
--- a/src/math/big/int.go
+++ b/src/math/big/int.go
@@ -361,7 +361,7 @@
// and returns z and a boolean indicating success. If SetString fails,
// the value of z is undefined but the returned value is nil.
//
-// The base argument must be 0 or a value from 2 through MaxBase. If the base
+// The base argument must be 0 or a value between 2 and MaxBase. If the base
// is 0, the string prefix determines the actual conversion base. A prefix of
// ``0x'' or ``0X'' selects base 16; the ``0'' prefix selects base 8, and a
// ``0b'' or ``0B'' prefix selects base 2. Otherwise the selected base is 10.
diff --git a/src/math/big/natconv.go b/src/math/big/natconv.go
index b5c3773..022dcfe 100644
--- a/src/math/big/natconv.go
+++ b/src/math/big/natconv.go
@@ -60,7 +60,7 @@
// digit = "0" ... "9" | "a" ... "z" | "A" ... "Z" .
//
// Unless fracOk is set, the base argument must be 0 or a value between
-// 2 through MaxBase. If fracOk is set, the base argument must be one of
+// 2 and MaxBase. If fracOk is set, the base argument must be one of
// 0, 2, 10, or 16. Providing an invalid base argument leads to a run-
// time panic.
//
