bug 1151: add beginnings of curve25519_mul

https://bugs.libre-soc.org/show_bug.cgi?id=773#c1

diff --git a/src/openpower/decoder/isa/ed25519/curve25519_mul.py b/src/openpower/decoder/isa/ed25519/curve25519_mul.py
new file mode 100644 (file)
index 0000000..1b6d639
--- /dev/null
+++ b/src/openpower/decoder/isa/ed25519/curve25519_mul.py
@@ -0,0 +1,84 @@
+"""
+Copyright (C) 2023 2024 Luke Kenneth Casson Leighton <lkcl@lkcl.net>
+License: LGPLv3+
+Funding: NLnet NGI-ASSURE Project funded under EU grant agreement No 957073.
+"""
+
+"""
+start here... https://bugs.libre-soc.org/show_bug.cgi?id=773#c1
+
+t[0]  =  r0 * s0
+t[1]  =  r0 * s1 + r1 * s0;
+t[2]  =  r0 * s2 + r1 * s1 + r2 * s0;
+t[3]  =  r0 * s3 + r1 * s2 + r2 * s1 + r3 * s0;
+t[4]  =  r0 * s4 + r1 * s3 + r2 * s2 + r3 * s1 + r4 * s0;
+
+       r1 *= 19;
+       r2 *= 19;
+       r3 *= 19;
+       r4 *= 19;
+
+t[0] += r4 * s1 + r3 * s2 + r2 * s3 + r1 * s4;
+t[1] += r4 * s2 + r3 * s3 + r2 * s4;
+t[2] += r4 * s3 + r3 * s4;
+t[3] += r4 * s4;
+
+                     r0 = lo128(t[0]) & reduce_mask_51; shr128(c, t[0], 51);
+add128_64(t[1], c)   r1 = lo128(t[1]) & reduce_mask_51; shr128(c, t[1], 51);
+add128_64(t[2], c)   r2 = lo128(t[2]) & reduce_mask_51; shr128(c, t[2], 51);
+add128_64(t[3], c)   r3 = lo128(t[3]) & reduce_mask_51; shr128(c, t[3], 51);
+add128_64(t[4], c)   r4 = lo128(t[4]) & reduce_mask_51; shr128(c, t[4], 51);
+r0 +=   c * 19; c = r0 >> 51; r0 = r0 & reduce_mask_51;
+r1 +=   c;
+
+"""
+
+import random
+
+def curve25519_mul(r, s):
+
+    t = [0] * 5
+
+    for i in range(5):
+        print("t%d += " % i, end='')
+        for j in range(i+1):
+            sidx = i-j
+            print("r%d*s%d + " % (i, sidx), end='')
+            t[i] += r[i] * s[sidx]
+        print()
+
+    for i in range(1,5):
+        r[i] *= 19
+
+    print()
+    for i in range(4,0,-1):
+        tidx = 4-i
+        print("t%d += " % tidx, end='')
+        for j in range(i):
+            jidx, sidx = 4-j, 5-(i-j)
+            print("r%d*s%d + " % (jidx, sidx), end='')
+            t[tidx] += r[jidx] * s[sidx]
+        print()
+
+    # this is the one where i *think* it possible to do some sort
+    # of single-operation similar to dsld.
+
+    c = 0
+    for i in range(5):
+        add128_64(t[i], c);
+        r[i] = lo128(t[i]) & reduce_mask_51;
+        shr128(c, t[i], 51);
+
+    r[0] +=   c * 19; c = r[0] >> 51; r[0] = r[0] & reduce_mask_51;
+    r[1] +=   c;
+
+if __name__ == '__main__':
+    random.seed(2) # set the same seed (consistent test)
+    r, s = [], []
+    for j in range(5):
+        r.append(random.randint(0, 2^50))
+        s.append(random.randint(0, 2^50))
+    print ("r", r)
+    print ("s", s)
+    t = curve25519_mul(r, s)
+    print ("t", t)