Zvk: Implement Zvkg, Vector GCM/GMAC instruction

Implement the proposed instruction in Zvkg, vghmac.vv,
Vector Carryless Multiply Accumulate over GHASH Galois-Field.

The instruction performs one step of GHASH routine as described
in "NIST Special Publication 800-38D" a.k.a the AES-GCM specification.
The logic was written to closely track the pseudo-code
in the Zvk specification.

Signed-off-by: Eric Gouriou <ego@rivosinc.com>
Co-authored-by: Kornel Duleba <mindal@semihalf.com>
Signed-off-by: Eric Gouriou <ego@rivosinc.com>

riscv/insns/vghsh_vv.h

@@ -0,0 +1,38 @@
+// vghsh.vv vd, vs2, vs1
+
+#include "zvk_ext_macros.h"
+
+require_zvkg;
+require(P.VU.vsew == 32);
+require_egw_fits(128);
+
+VI_ZVK_VD_VS1_VS2_EGU32x4_NOVM_LOOP(
+  {},
+  {
+    EGU32x4_t Y = vd;   // Current partial hash
+    EGU32x4_t X = vs1;  // Block cipher output
+    EGU32x4_t H = vs2;  // Hash subkey
+
+    EGU32x4_BREV8(H);
+    EGU32x4_t Z = {};
+
+    // S = brev8(Y ^ X)
+    EGU32x4_t S;
+    EGU32x4_XOR(S, Y, X);
+    EGU32x4_BREV8(S);
+
+    for (int bit = 0; bit < 128; bit++) {
+      if (EGU32x4_ISSET(S, bit)) {
+        EGU32x4_XOREQ(Z, H);
+      }
+
+      const bool reduce = EGU32x4_ISSET(H, 127);
+      EGU32x4_LSHIFT(H);  // Left shift by 1.
+      if (reduce) {
+        H[0] ^= 0x87; // Reduce using x^7 + x^2 + x^1 + 1 polynomial
+      }
+    }
+    EGU32x4_BREV8(Z);
+    vd = Z;
+  }
+);

riscv/insns/vgmul_vv.h

@@ -0,0 +1,32 @@
+// vgmul.vv vd, vs2
+
+#include "zvk_ext_macros.h"
+
+require_zvkg;
+require(P.VU.vsew == 32);
+require_egw_fits(128);
+
+VI_ZVK_VD_VS2_EGU32x4_NOVM_LOOP(
+  {},
+  {
+    EGU32x4_t Y = vd;  // Multiplier
+    EGU32x4_BREV8(Y);
+    EGU32x4_t H = vs2;  // Multiplicand
+    EGU32x4_BREV8(H);
+    EGU32x4_t Z = {};
+
+    for (int bit = 0; bit < 128; bit++) {
+      if (EGU32x4_ISSET(Y, bit)) {
+        EGU32x4_XOREQ(Z, H);
+      }
+
+      bool reduce = EGU32x4_ISSET(H, 127);
+      EGU32x4_LSHIFT(H);  // Lef shift by 1
+      if (reduce) {
+        H[0] ^= 0x87; // Reduce using x^7 + x^2 + x^1 + 1 polynomial
+      }
+    }
+    EGU32x4_BREV8(Z);
+    vd = Z;
+  }
+);

riscv/riscv.mk.in

@@ -1364,9 +1364,14 @@ riscv_insn_ext_zvbc = \
 	vclmulh_vv \
 	vclmulh_vx \
 
+riscv_insn_ext_zvkg= \
+	vghsh_vv \
+	vgmul_vv \
+
 riscv_insn_ext_zvk = \
 	$(riscv_insn_ext_zvbb) \
 	$(riscv_insn_ext_zvbc) \
+	$(riscv_insn_ext_zvkg) \
 
 riscv_insn_list = \
 	$(if $(HAVE_INT128),$(riscv_insn_ext_v),) \

riscv/zvk_ext_macros.h

@@ -942,8 +942,8 @@
 // Performs  "MUT_A ^= CONST_B;", i.e., xor of the bytes
 // in A (mutated) with the bytes in B (unchanged).
 #define EGU32x4_XOREQ(MUT_A, CONST_B) \
-  for (std::size_t bidx = 0; bidx < 4; ++bidx) { \
-    (MUT_A)[bidx] ^= (CONST_B)[bidx]; \
+  for (std::size_t idx = 0; idx < 4; ++idx) { \
+    (MUT_A)[idx] ^= (CONST_B)[idx]; \
   }
 
 // Performs  "DST = A ^ B;", i.e., DST (overwritten) receives
@@ -953,6 +953,18 @@
     (DST)[bidx] = (A)[bidx] ^ (B)[bidx]; \
   }
 
+// Performs  "DST = A ^ B;", i.e., DST (overwritten) receives
+// the xor of the bytes in A and B (both unchanged).
+#define EGU32x4_XOR(DST, A, B) \
+  do { \
+    static_assert(std::is_same<EGU32x4_t, decltype(A)>::value); \
+    static_assert(std::is_same<EGU32x4_t, decltype(B)>::value); \
+    static_assert(std::is_same<EGU32x4_t, decltype(DST)>::value); \
+    for (std::size_t idx = 0; idx < 4; ++idx) { \
+      (DST)[idx] = (A)[idx] ^ (B)[idx]; \
+    } \
+  } while (0)
+
 //
 // Common bit manipulations logic.
 //