[libc] [llvm] [libc] Refactor `BigInt` (PR #86137)

[Clement Courbet via llvm-commits]

================
@@ -8,13 +8,198 @@
 
 #include "src/__support/CPP/optional.h"
 #include "src/__support/UInt.h"
+#include "src/__support/integer_literals.h"        // parse_unsigned_bigint
 #include "src/__support/macros/properties/types.h" // LIBC_TYPES_HAS_INT128
 
 #include "include/llvm-libc-macros/math-macros.h" // HUGE_VALF, HUGE_VALF
 #include "test/UnitTest/Test.h"
 
 namespace LIBC_NAMESPACE {
 
+enum Value { ZERO, ONE, TWO, MIN, MAX };
+
+template <typename T> auto create(Value value) {
+  switch (value) {
+  case ZERO:
+    return T(0);
+  case ONE:
+    return T(1);
+  case TWO:
+    return T(2);
+  case MIN:
+    return T::min();
+  case MAX:
+    return T::max();
+  }
+}
+
+using Types = testing::TypeList< //
+#ifdef LIBC_TYPES_HAS_INT64
+    BigInt<64, false, uint64_t>, // 64-bits unsigned (1 x uint64_t)
+    BigInt<64, true, uint64_t>,  // 64-bits   signed (1 x uint64_t)
+#endif
+#ifdef LIBC_TYPES_HAS_INT128
+    BigInt<128, false, __uint128_t>, // 128-bits unsigned (1 x __uint128_t)
+    BigInt<128, true, __uint128_t>,  // 128-bits   signed (1 x __uint128_t)
+#endif
+    BigInt<16, false, uint16_t>, // 16-bits unsigned (1 x uint16_t)
+    BigInt<16, true, uint16_t>,  // 16-bits   signed (1 x uint16_t)
+    BigInt<64, false, uint16_t>, // 64-bits unsigned (4 x uint16_t)
+    BigInt<64, true, uint16_t>   // 64-bits   signed (4 x uint16_t)
+    >;
+
+#define ASSERT_SAME(A, B) ASSERT_TRUE((A) == (B))
+
+TYPED_TEST(LlvmLibcUIntClassTest, Additions, Types) {
+  ASSERT_SAME(create<T>(ZERO) + create<T>(ZERO), create<T>(ZERO));
+  ASSERT_SAME(create<T>(ONE) + create<T>(ZERO), create<T>(ONE));
+  ASSERT_SAME(create<T>(ZERO) + create<T>(ONE), create<T>(ONE));
+  ASSERT_SAME(create<T>(ONE) + create<T>(ONE), create<T>(TWO));
+  // 2's complement addition works for signed and unsigned types.
+  // - unsigned : 0xff + 0x01 = 0x00 (255 + 1 = 0)
+  // -   signed : 0xef + 0x01 = 0xf0 (127 + 1 = -128)
+  ASSERT_SAME(create<T>(MAX) + create<T>(ONE), create<T>(MIN));
+}
+
+TYPED_TEST(LlvmLibcUIntClassTest, Subtraction, Types) {
+  ASSERT_SAME(create<T>(ZERO) - create<T>(ZERO), create<T>(ZERO));
+  ASSERT_SAME(create<T>(ONE) - create<T>(ONE), create<T>(ZERO));
+  ASSERT_SAME(create<T>(ONE) - create<T>(ZERO), create<T>(ONE));
+  // 2's complement subtraction works for signed and unsigned types.
+  // - unsigned : 0x00 - 0x01 = 0xff (   0 - 1 = 255)
+  // -   signed : 0xf0 - 0x01 = 0xef (-128 - 1 = 127)
+  ASSERT_SAME(create<T>(MIN) - create<T>(ONE), create<T>(MAX));
+}
+
+TYPED_TEST(LlvmLibcUIntClassTest, Multiplication, Types) {
+  ASSERT_SAME(create<T>(ZERO) * create<T>(ZERO), create<T>(ZERO));
+  ASSERT_SAME(create<T>(ZERO) * create<T>(ONE), create<T>(ZERO));
+  ASSERT_SAME(create<T>(ONE) * create<T>(ZERO), create<T>(ZERO));
+  ASSERT_SAME(create<T>(ONE) * create<T>(ONE), create<T>(ONE));
+  ASSERT_SAME(create<T>(ONE) * create<T>(TWO), create<T>(TWO));
+  ASSERT_SAME(create<T>(TWO) * create<T>(ONE), create<T>(TWO));
+  // - unsigned : 0xff x 0xff = 0x01 (mod 0xff)
+  // -   signed : 0xef x 0xef = 0x01 (mod 0xff)
+  ASSERT_SAME(create<T>(MAX) * create<T>(MAX), create<T>(ONE));
+}
+
+template <typename T> void print(const char *msg, T value) {
+  testing::tlog << msg;
+  IntegerToString<T, radix::Hex> buffer(value);
+  testing::tlog << buffer.view() << "\n";
+}
+
+TEST(LlvmLibcUIntClassTest, SignedAddSub) {
+  // Computations performed by https://www.wolframalpha.com/
+  using T = BigInt<128, true, uint32_t>;
+  const T a = parse_bigint<T>("1927508279017230597");
+  const T b = parse_bigint<T>("278789278723478925");
+  const T s = parse_bigint<T>("2206297557740709522");
+  // Addition
+  ASSERT_SAME(a + b, s);
+  ASSERT_SAME(b + a, s); // commutative
+  // Subtraction
+  ASSERT_SAME(a - s, -b);
+  ASSERT_SAME(s - a, b);
+}
+
+TEST(LlvmLibcUIntClassTest, SignedMulDiv) {
+  // Computations performed by https://www.wolframalpha.com/
+  using T = BigInt<128, true, uint16_t>;
+  struct {
+    const char *a;
+    const char *b;
+    const char *mul;
+  } const test_cases[] = {{"-4", "3", "-12"},
----------------
legrosbuffle wrote:

Suggestion: write a fuzz test that takes 2x8 bytes, inteprets them as 2 int64s, computes native and `Bigint<uint8>` implementations of `add`/`div/`mul`, and compares those.

https://github.com/llvm/llvm-project/pull/86137