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math/big: reduce allocations in Karatsuba case of sqr
For #23221. Change-Id: If55dcf2e0706d6658f4a0863e3740437e008706c Reviewed-on: https://go-review.googlesource.com/114335 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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@ -512,8 +512,7 @@ func karatsubaSqr(z, x nat) {
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n := len(x)
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if n&1 != 0 || n < karatsubaSqrThreshold || n < 2 {
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z = z[:2*n]
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basicSqr(z, x)
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basicSqr(z[:2*n], x)
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return
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}
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@ -562,13 +561,14 @@ func (z nat) sqr(x nat) nat {
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if alias(z, x) {
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z = nil // z is an alias for x - cannot reuse
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}
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z = z.make(2 * n)
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if n < basicSqrThreshold {
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z = z.make(2 * n)
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basicMul(z, x, x)
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return z.norm()
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}
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if n < karatsubaSqrThreshold {
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z = z.make(2 * n)
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basicSqr(z, x)
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return z.norm()
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}
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