7818b82fc8
Updates #22830 Due to not checking if the output slices alias in divLarge, calls of the form z.div(z, x, y) caused the slice z to attempt to be used to store both the quotient and the remainder of the division. CL 78995 applies an alias check to correct that error. This CL cleans up the additional div calls that attempt to supply the same slice to hold both the quotient and remainder. Note that the call in expNN was responsible for the reported error in r.Exp(x, 1, m) when r was initialized to a non-zero value. The second instance in expNNMontgomery did not result in an error due to the size of the arguments. // RR = 2**(2*_W*len(m)) mod m RR := nat(nil).setWord(1) zz := nat(nil).shl(RR, uint(2*numWords*_W)) _, RR = RR.div(RR, zz, m) Specifically, cap(RR) == 5 after setWord(1) due to const e = 4 in z.make(1) len(zz) == 2*len(m) + 1 after shifting left, numWords = len(m) Reusing the backing array for z and z2 in div was only triggered if cap(RR) >= len(zz) + 1 and len(m) > 1 so that divLarge was called. But, 5 < 2*len(m) + 2 if len(m) > 1, so new arrays were allocated and the error was never triggered in this case. Change-Id: Iedac80dbbde13216c94659e84d28f6f4be3aaf24 Reviewed-on: https://go-review.googlesource.com/81055 Run-TryBot: Robert Griesemer <gri@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Robert Griesemer <gri@golang.org> |
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