math/big: permit upper-case 'P' binary exponent (not just 'p')

The current implementation accepted binary exponents but restricted
them to 'p'. This change permits both 'p' and 'P'.

R=Go1.13

Updates #29008.

Change-Id: I7a89ccb86af4438f17b0422be7cb630ffcf43272
Reviewed-on: https://go-review.googlesource.com/c/159297Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

src/math/big/floatconv.go

@@ -224,7 +224,7 @@ func (z *Float) pow5(n uint64) *Float {
 //	sign     = "+" | "-" .
 //	prefix   = "0" ( "x" | "X" | "b" | "B" ) .
 //	mantissa = digits | digits "." [ digits ] | "." digits .
-//	exponent = ( "E" | "e" | "p" ) [ sign ] digits .
+//	exponent = ( "e" | "E" | "p" | "P" ) [ sign ] digits .
 //	digits   = digit { digit } .
 //	digit    = "0" ... "9" | "a" ... "z" | "A" ... "Z" .
 //	infinity = [ sign ] ( "inf" | "Inf" ) .
@@ -238,7 +238,7 @@ func (z *Float) pow5(n uint64) *Float {
 // The octal prefix "0" is not supported (a leading "0" is simply
 // considered a "0").
 //
-// A "p" exponent indicates a binary (rather then decimal) exponent;
+// A "p" or "P" exponent indicates a binary (rather then decimal) exponent;
 // for instance "0x1.fffffffffffffp1023" (using base 0) represents the
 // maximum float64 value. For hexadecimal mantissae, the exponent must
 // be binary, if present (an "e" or "E" exponent indicator cannot be

src/math/big/floatconv_test.go

@@ -108,6 +108,7 @@ func TestFloatSetFloat64String(t *testing.T) {
 		{"0b001p-3", 0.125},
 		{"0b.001p3", 1},
 		{"0b0.01p2", 1},
+		{"0b0.01P+2", 1},
 
 		// hexadecimal mantissa and exponent
 		{"0x0", 0},
@@ -117,6 +118,7 @@ func TestFloatSetFloat64String(t *testing.T) {
 		{"0xff", 255},
 		{"0X.8p1", 1},
 		{"-0X0.00008p16", -0.5},
+		{"-0X0.00008P+16", -0.5},
 		{"0x0.0000000000001p-1022", math.SmallestNonzeroFloat64},
 		{"0x1.fffffffffffffp1023", math.MaxFloat64},
 	} {

src/math/big/ratconv.go

@@ -130,10 +130,10 @@ func (z *Rat) SetString(s string) (*Rat, bool) {
 }
 
 // scanExponent scans the longest possible prefix of r representing a decimal
-// ('e', 'E') or binary ('p') exponent, if any. It returns the exponent, the
-// exponent base (10 or 2), or a read or syntax error, if any.
+// ('e', 'E') or binary ('p', 'P') exponent, if any. It returns the exponent,
+// the exponent base (10 or 2), or a read or syntax error, if any.
 //
-//	exponent = ( "E" | "e" | "p" ) [ sign ] digits .
+//	exponent = ( "e" | "E" | "p" | "P" ) [ sign ] digits .
 //	sign     = "+" | "-" .
 //	digits   = digit { digit } .
 //	digit    = "0" ... "9" .
@@ -153,7 +153,7 @@ func scanExponent(r io.ByteScanner, binExpOk bool) (exp int64, base int, err err
 	switch ch {
 	case 'e', 'E':
 		// ok
-	case 'p':
+	case 'p', 'P':
 		if binExpOk {
 			base = 2
 			break // ok