From: Jacob Lifshay <programmerjake@gmail.com>
Date: Fri, 22 Dec 2023 05:10:11 +0000 (-0800)
Subject: tests/bigint/powmod: initial version of bigint multiply remap
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=a3c1930de7990c8babcb3908ed7650e1d08eafb6;p=openpower-isa.git

tests/bigint/powmod: initial version of bigint multiply remap

it has some issues around being able to encode scalar RS but
vector RT, and doesn't match the scalar * vector multiplication
pattern, but is quite compact.
---

diff --git a/src/openpower/test/bigint/powmod.py b/src/openpower/test/bigint/powmod.py
index 7fc79468..73d87b35 100644
--- a/src/openpower/test/bigint/powmod.py
+++ b/src/openpower/test/bigint/powmod.py
@@ -99,32 +99,35 @@ def python_mul_algorithm(a, b):
     return y
 
 
-def python_mul_algorithm2(a, b):
+def python_mul_remap_algorithm(a, b):
     # version 2 of the MUL_256_X_256_TO_512_ASM algorithm using base 100 rather
     # than 2^64, since that's easier to read.
-    # the idea here is that it will "morph" into something more akin to
-    # using REMAP bigmul (first using REMAP Indexed)
-
-    # create a schedule for use below. the "end of inner loop" marker is 0b01
-    iyl = []
-    il = []
-    for iy in range(4):
-        for i in range(4):
-            iyl.append((iy+i, i == 3))
-            il.append(i)
-        for i in range(5):
-            iyl.append((iy+i, i == 4))
-            il.append(i)
-
-    y = [0] * 8  # result y and temp t of same size
-    t = [0] * 8  # no need after this to set t[4] to zero
-    for iy in range(4):
-        for i in range(4):  # use t[iy+4] as a 64-bit carry
-            t[iy+i], t[iy+4] = maddedu(a[iy], b[i], t[iy+4])
-        ca = 0
-        for i in range(5):  # add vec t to y with 1-bit carry
-            idx = iy + i
-            y[idx], ca = adde(y[idx], t[idx], ca)
+    # run this file in a debugger to see all the intermediate values.
+    a_sz = len(a)
+    b_sz = len(b)
+    a_idx = []
+    b_idx = []
+    a_plus_b_idx = []
+    a_plus_b_plus_1_idx = []
+    for ai in range(a_sz):
+        for bi in range(b_sz):
+            a_idx.append(ai)
+            b_idx.append(bi)
+            a_plus_b_idx.append(ai + bi)
+            a_plus_b_plus_1_idx.append(ai + bi + 1)
+
+    y = [0] * (a_sz + b_sz)
+    ca = 0
+    for i in range(a_sz * b_sz):
+        # no need to clear ca between ai outer loops, since the partial
+        # products can't get big enough to have a carry out, so ca will
+        # always be zero when (i % b_sz == 0).
+        # That said, hardware will probably want to pattern-match this to
+        # remove the unnecessary dependency through ca.
+        y[a_plus_b_idx[i]], t = maddedu(
+            a[a_idx[i]], b[b_idx[i]], y[a_plus_b_idx[i]])
+        y[a_plus_b_plus_1_idx[i]], ca = adde(
+            y[a_plus_b_plus_1_idx[i]], t, ca)
     return y
 
 
@@ -1255,19 +1258,26 @@ if __name__ == "__main__":
     a = b = (99, 99, 99, 99)
     expected = [1, 0, 0, 0, 98, 99, 99, 99]
     assert python_mul_algorithm(a, b) == expected
+    # check python_mul_remap_algorithm
+    assert python_mul_remap_algorithm(a, b) == expected
 
-    # now test python_mul_algorithm2 *against* python_mul_algorithm
+    # now test python_mul_remap_algorithm *against* python_mul_algorithm
     import random
     random.seed(0)  # reproducible values
-    for i in range(10000):
+
+    def fmt_l(l):
+        return "[" + ", ".join("%2i" % (i,) for i in l) + "]"
+
+    for i in range(100000):
         a = []
         b = []
         for j in range(4):
             a.append(random.randint(0, 99))
             b.append(random.randint(0, 99))
         expected = python_mul_algorithm(a, b)
-        testing = python_mul_algorithm2(a, b)
-        report = "%+17s * %-17s = %s\n" % (repr(a), repr(b), repr(expected))
-        report += "                                       (%s)" % repr(testing)
+        testing = python_mul_remap_algorithm(a, b)
+        report = "%s * %s = " % (fmt_l(a), fmt_l(b))
+        indent = " " * len(report)
+        report += "%s\n%s%s" % (fmt_l(expected), indent, fmt_l(testing))
         print(report)
         assert expected == testing