Import gcrypt public-key cryptography and implement signature checking.

grub-core/lib/libgcrypt/mpi/hppa/README

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+This directory contains mpn functions for various HP PA-RISC chips.  Code
+that runs faster on the PA7100 and later implementations, is in the pa7100
+directory.
+
+RELEVANT OPTIMIZATION ISSUES
+
+  Load and Store timing
+
+On the PA7000 no memory instructions can issue the two cycles after a store.
+For the PA7100, this is reduced to one cycle.
+
+The PA7100 has a lookup-free cache, so it helps to schedule loads and the
+dependent instruction really far from each other.
+
+STATUS
+
+1. mpn_mul_1 could be improved to 6.5 cycles/limb on the PA7100, using the
+   instructions bwlow (but some sw pipelining is needed to avoid the
+   xmpyu-fstds delay):
+
+	fldds	s1_ptr
+
+	xmpyu
+	fstds	N(%r30)
+	xmpyu
+	fstds	N(%r30)
+
+	ldws	N(%r30)
+	ldws	N(%r30)
+	ldws	N(%r30)
+	ldws	N(%r30)
+
+	addc
+	stws	res_ptr
+	addc
+	stws	res_ptr
+
+	addib	Loop
+
+2. mpn_addmul_1 could be improved from the current 10 to 7.5 cycles/limb
+   (asymptotically) on the PA7100, using the instructions below.  With proper
+   sw pipelining and the unrolling level below, the speed becomes 8
+   cycles/limb.
+
+	fldds	s1_ptr
+	fldds	s1_ptr
+
+	xmpyu
+	fstds	N(%r30)
+	xmpyu
+	fstds	N(%r30)
+	xmpyu
+	fstds	N(%r30)
+	xmpyu
+	fstds	N(%r30)
+
+	ldws	N(%r30)
+	ldws	N(%r30)
+	ldws	N(%r30)
+	ldws	N(%r30)
+	ldws	N(%r30)
+	ldws	N(%r30)
+	ldws	N(%r30)
+	ldws	N(%r30)
+	addc
+	addc
+	addc
+	addc
+	addc	%r0,%r0,cy-limb
+
+	ldws	res_ptr
+	ldws	res_ptr
+	ldws	res_ptr
+	ldws	res_ptr
+	add
+	stws	res_ptr
+	addc
+	stws	res_ptr
+	addc
+	stws	res_ptr
+	addc
+	stws	res_ptr
+
+	addib