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crypto/elliptic: reduce allocations in s390x P256 code
The Go compiler assumes that pointers escape when passed into assembly functions. To override this behavior we can annotate assembly functions with go:noescape, telling the compiler that we know pointers do not escape from it. By annotating the assembly functions in the s390x P256 code in this way we enable more variables to be allocated on the stack rather than the heap, reducing the number of heap allocations required to execute this code: name old alloc/op new alloc/op delta SignP256 3.66kB ± 0% 2.64kB ± 0% -27.95% (p=0.008 n=5+5) VerifyP256 4.46kB ± 0% 1.23kB ± 0% -72.40% (p=0.008 n=5+5) name old allocs/op new allocs/op delta SignP256 40.0 ± 0% 31.0 ± 0% -22.50% (p=0.008 n=5+5) VerifyP256 41.0 ± 0% 24.0 ± 0% -41.46% (p=0.008 n=5+5) Change-Id: Id526c30c9b04b2ad79a55d76cab0e30cc8d60402 Reviewed-on: https://go-review.googlesource.com/66230 Run-TryBot: Michael Munday <mike.munday@ibm.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org>
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@ -50,6 +50,8 @@ func (curve p256CurveFast) Params() *CurveParams {
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// Functions implemented in p256_asm_s390x.s
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// Montgomery multiplication modulo P256
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//
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//go:noescape
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func p256MulAsm(res, in1, in2 []byte)
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// Montgomery square modulo P256
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@ -58,19 +60,31 @@ func p256Sqr(res, in []byte) {
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}
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// Montgomery multiplication by 1
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//
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//go:noescape
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func p256FromMont(res, in []byte)
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// iff cond == 1 val <- -val
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//
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//go:noescape
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func p256NegCond(val *p256Point, cond int)
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// if cond == 0 res <- b; else res <- a
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//
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//go:noescape
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func p256MovCond(res, a, b *p256Point, cond int)
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// Constant time table access
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//
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//go:noescape
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func p256Select(point *p256Point, table []p256Point, idx int)
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//go:noescape
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func p256SelectBase(point *p256Point, table []p256Point, idx int)
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// Montgomery multiplication modulo Ord(G)
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//
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//go:noescape
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func p256OrdMul(res, in1, in2 []byte)
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// Montgomery square modulo Ord(G), repeated n times
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@ -85,10 +99,16 @@ func p256OrdSqr(res, in []byte, n int) {
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// If sign == 1 -> P2 = -P2
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// If sel == 0 -> P3 = P1
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// if zero == 0 -> P3 = P2
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//
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//go:noescape
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func p256PointAddAffineAsm(P3, P1, P2 *p256Point, sign, sel, zero int)
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// Point add
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//
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//go:noescape
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func p256PointAddAsm(P3, P1, P2 *p256Point) int
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//go:noescape
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func p256PointDoubleAsm(P3, P1 *p256Point)
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func (curve p256CurveFast) Inverse(k *big.Int) *big.Int {
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