pkg/math: fix Log2E and Log10E constant expressions

They were a division of integer constants, which got truncated,
meaning that Log2E rounded down to 1 and Log10E to 0.

To force them to be floating-point constants, like the CUE ones,
turn the dividend into a floating-point constant.

I found this problem since staticcheck correctly pointed out
a constant integer division which resulted in zero:

    math.go:156:11: the integer division '100… / 230…' results in zero (SA4025)

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>
Change-Id: I36ee54a7c8aff06368016b855536a9614dbbf229
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/557322
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
Reviewed-by: Paul Jolly <paul@myitcv.io>

pkg/math/math.go

@@ -151,9 +151,9 @@ const (
 	SqrtPhi = 1.27201964951406896425242246173749149171560804184009624861664038 // https://oeis.org/A139339
 
 	Ln2    = 0.693147180559945309417232121458176568075500134360255254120680009 // https://oeis.org/A002162
-	Log2E  = 1000000000000000000000000000000000000000000000000000000000000000 / 693147180559945309417232121458176568075500134360255254120680009
+	Log2E  = 1000000000000000000000000000000000000000000000000000000000000000.0 / 693147180559945309417232121458176568075500134360255254120680009
 	Ln10   = 2.30258509299404568401799145468436420760110148862877297603332790 // https://oeis.org/A002392
-	Log10E = 10000000000000000000000000000000000000000000000000000000000000 / 23025850929940456840179914546843642076011014886287729760333279
+	Log10E = 10000000000000000000000000000000000000000000000000000000000000.0 / 23025850929940456840179914546843642076011014886287729760333279
 )
 
 // Copysign returns a value with the magnitude

pkg/math/math_test.go

@@ -54,7 +54,7 @@ func Example_constants() {
 	//  SqrtPi: 1.772453850905516
 	// SqrtPhi: 1.272019649514069
 	//     Ln2: 0.6931471805599453
-	//   Log2E: 1
+	//   Log2E: 1.4426950408889634
 	//    Ln10: 2.302585092994046
-	//  Log10E: 0
+	//  Log10E: 0.4342944819032518
 }