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math: correct mPi4 comment 

The previous comment mis-stated the number of bits in mPi4.
The correct value is 19*64 + 1 == 1217 bits.

Change-Id: Ife971ff6936ce2d5b81ce663ce48044749d592a0
Reviewed-on: https://go-review.googlesource.com/c/154017
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Brian Kessler 2018-12-13 09:19:11 -07:00 committed by Robert Griesemer
parent d177e10d22
commit 02ad841dd8
1 changed files with 2 additions and 2 deletions
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4
src/math/trig_reduce.go
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@ -68,8 +68,8 @@ func trigReduce(x float64) (j uint64, z float64) {
// mPi4 is the binary digits of 4/pi as a uint64 array, // mPi4 is the binary digits of 4/pi as a uint64 array,
// that is, 4/pi = Sum mPi4[i]*2^(-64*i) // that is, 4/pi = Sum mPi4[i]*2^(-64*i)
// 19 64-bit digits gives 1153 bits of precision to handle // 19 64-bit digits and the leading one bit give 1217 bits
// the largest possible float64 exponent. // of precision to handle the largest possible float64 exponent.
var mPi4 = [...]uint64{ var mPi4 = [...]uint64{
0x0000000000000001, 0x0000000000000001,
0x45f306dc9c882a53, 0x45f306dc9c882a53,