add function and test of the inverse of f_2^128 (#359)

* add function and test of the inverse of f_2^128 * update format * simplify the inv * simplify the inv
secretflow · Jul 10, 2024 · cf2737c · cf2737c
1 parent e230ae7
commit cf2737c
Show file tree

Hide file tree

Showing 2 changed files with 37 additions and 0 deletions.
diff --git a/yacl/math/f2k/f2k.h b/yacl/math/f2k/f2k.h
@@ -189,6 +189,31 @@ inline uint64_t GfInv64(uint64_t x) {
   return t0;
 }
 
+// inverse over Galois Field F_{2^128}
+inline uint128_t GfInv128(uint128_t x) {
+  uint128_t t0 = GfMul128(x, x);
+  uint128_t t1 = t0;
+  t0 = GfMul128(t0, t0);
+  t1 = GfMul128(t1, t0);
+  t0 = GfMul128(t0, t0);
+  t1 = GfMul128(t1, t0);
+  t0 = GfMul128(t0, t0);
+  t1 = GfMul128(t1, t0);
+  t0 = GfMul128(t0, t0);
+  t1 = GfMul128(t1, t0);
+  t0 = GfMul128(t0, t0);
+  t1 = GfMul128(t1, t0);
+  t0 = GfMul128(t0, t0);
+  t1 = GfMul128(t1, t0);
+  for (int i = 0; i < 60; i++) {
+    t0 = GfMul128(t0, t0);
+    t1 = GfMul128(t1, t0);
+    t0 = GfMul128(t0, t0);
+    t1 = GfMul128(t1, t0);
+  }
+  return t1;
+}
+
 // Inner product <x,y>
 inline std::pair<uint128_t, uint128_t> ClMul128(absl::Span<const uint128_t> x,
                                                 absl::Span<const uint128_t> y) {

diff --git a/yacl/math/f2k/f2k_test.cc b/yacl/math/f2k/f2k_test.cc
@@ -139,4 +139,16 @@ TEST(F2kTest, GfInv64_inner_product) {
     auto check = yacl::GfMul64(x[i], inv);
     EXPECT_EQ(uint64_t(1), check);
   }
+}
+
+// test for the inverse of 128-bit field
+TEST(F2kTest, GfInv128_inner_product) {
+  const uint64_t size = 1001;
+
+  auto x = yacl::crypto::RandVec<uint128_t>(size);
+  for (uint128_t i = 0; i < size; ++i) {
+    auto inv = yacl::GfInv128(x[i]);
+    auto check = yacl::GfMul128(x[i], inv);
+    EXPECT_EQ(uint128_t(1), check);
+  }
 }