Add support for `u128`, `U128`, `s128` and `S128` integers to `IO::Buffer`. (#15399)

6 files changed, 492 insertions, 3 deletions

diff --git a/bignum.c b/bignum.c
index 8d3eac8e0a..ed53d75149 100644
--- a/bignum.c
+++ b/bignum.c
@@ -4515,7 +4515,7 @@ rb_str2big_gmp(VALUE arg, int base, int badcheck)
 
 #if HAVE_LONG_LONG
 
-static VALUE
+VALUE
 rb_ull2big(unsigned LONG_LONG n)
 {
     long i;
@@ -4537,7 +4537,7 @@ rb_ull2big(unsigned LONG_LONG n)
     return big;
 }
 
-static VALUE
+VALUE
 rb_ll2big(LONG_LONG n)
 {
     long neg = 0;
@@ -4575,7 +4575,7 @@ rb_ll2inum(LONG_LONG n)
 #endif  /* HAVE_LONG_LONG */
 
 #ifdef HAVE_INT128_T
-static VALUE
+VALUE
 rb_uint128t2big(uint128_t n)
 {
     long i;
diff --git a/internal/bignum.h b/internal/bignum.h
index e5b6b42563..0692bafed3 100644
--- a/internal/bignum.h
+++ b/internal/bignum.h
@@ -169,7 +169,13 @@ VALUE rb_str2big_gmp(VALUE arg, int base, int badcheck);
 VALUE rb_int_parse_cstr(const char *str, ssize_t len, char **endp, size_t *ndigits, int base, int flags);
 RUBY_SYMBOL_EXPORT_END
 
+#if HAVE_LONG_LONG
+VALUE rb_ull2big(unsigned LONG_LONG n);
+VALUE rb_ll2big(LONG_LONG n);
+#endif
+
 #if defined(HAVE_INT128_T)
+VALUE rb_uint128t2big(uint128_t n);
 VALUE rb_int128t2big(int128_t n);
 #endif
 
diff --git a/internal/numeric.h b/internal/numeric.h
index 58f42f41ac..75181a7f16 100644
--- a/internal/numeric.h
+++ b/internal/numeric.h
@@ -127,6 +127,49 @@ VALUE rb_int_bit_length(VALUE num);
 VALUE rb_int_uminus(VALUE num);
 VALUE rb_int_comp(VALUE num);
 
+// Unified 128-bit integer structures that work with or without native support:
+union rb_uint128 {
+#ifdef WORDS_BIGENDIAN
+    struct {
+        uint64_t high;
+        uint64_t low;
+    } parts;
+#else
+    struct {
+        uint64_t low;
+        uint64_t high;
+    } parts;
+#endif
+#ifdef HAVE_UINT128_T
+    uint128_t value;
+#endif
+};
+typedef union rb_uint128 rb_uint128_t;
+
+union rb_int128 {
+#ifdef WORDS_BIGENDIAN
+    struct {
+        uint64_t high;
+        uint64_t low;
+    } parts;
+#else
+    struct {
+        uint64_t low;
+        uint64_t high;
+    } parts;
+#endif
+#ifdef HAVE_UINT128_T
+    int128_t value;
+#endif
+};
+typedef union rb_int128 rb_int128_t;
+
+// Conversion functions for 128-bit integers:
+rb_uint128_t rb_numeric_to_uint128(VALUE x);
+rb_int128_t rb_numeric_to_int128(VALUE x);
+VALUE rb_uint128_to_numeric(rb_uint128_t n);
+VALUE rb_int128_to_numeric(rb_int128_t n);
+
 static inline bool
 INT_POSITIVE_P(VALUE num)
 {
diff --git a/io_buffer.c b/io_buffer.c
index 89f169176f..0d2cbdb4b7 100644
--- a/io_buffer.c
+++ b/io_buffer.c
@@ -1864,6 +1864,9 @@ io_buffer_validate_type(size_t size, size_t offset)
 // :u64, :U64 | unsigned 64-bit integer.
 // :s64, :S64 | signed 64-bit integer.
 //
+// :u128, :U128 | unsigned 128-bit integer.
+// :s128, :S128 | signed 128-bit integer.
+//
 // :f32, :F32 | 32-bit floating point number.
 // :f64, :F64 | 64-bit floating point number.
 
@@ -1895,6 +1898,45 @@ ruby_swapf64(double value)
     return swap.value;
 }
 
+// Structures and conversion functions are now in numeric.h/numeric.c
+// Unified swap function for 128-bit integers (works with both signed and unsigned)
+// Since both rb_uint128_t and rb_int128_t have the same memory layout,
+// we can use a union to make the swap function work with both types
+static inline rb_uint128_t
+ruby_swap128_uint(rb_uint128_t x)
+{
+    rb_uint128_t result;
+#ifdef HAVE_UINT128_T
+#if __has_builtin(__builtin_bswap128)
+    result.value = __builtin_bswap128(x.value);
+#else
+    // Manual byte swap for 128-bit integers
+    uint64_t low = (uint64_t)x.value;
+    uint64_t high = (uint64_t)(x.value >> 64);
+    low = ruby_swap64(low);
+    high = ruby_swap64(high);
+    result.value = ((uint128_t)low << 64) | high;
+#endif
+#else
+    // Fallback swap function using two 64-bit integers
+    // For big-endian data on little-endian host (or vice versa):
+    // 1. Swap bytes within each 64-bit part
+    // 2. Swap the order of the parts (since big-endian stores high first, little-endian stores low first)
+    result.parts.low = ruby_swap64(x.parts.high);
+    result.parts.high = ruby_swap64(x.parts.low);
+#endif
+    return result;
+}
+
+static inline rb_int128_t
+ruby_swap128_int(rb_int128_t x)
+{
+    // Cast to unsigned, swap, then cast back
+    rb_uint128_t u = *(rb_uint128_t*)&x;
+    rb_uint128_t swapped = ruby_swap128_uint(u);
+    return *(rb_int128_t*)&swapped;
+}
+
 #define IO_BUFFER_DECLARE_TYPE(name, type, endian, wrap, unwrap, swap) \
 static ID RB_IO_BUFFER_DATA_TYPE_##name; \
 \
@@ -1941,6 +1983,11 @@ IO_BUFFER_DECLARE_TYPE(U64, uint64_t, RB_IO_BUFFER_BIG_ENDIAN, RB_ULL2NUM, RB_NU
 IO_BUFFER_DECLARE_TYPE(s64, int64_t, RB_IO_BUFFER_LITTLE_ENDIAN, RB_LL2NUM, RB_NUM2LL, ruby_swap64)
 IO_BUFFER_DECLARE_TYPE(S64, int64_t, RB_IO_BUFFER_BIG_ENDIAN, RB_LL2NUM, RB_NUM2LL, ruby_swap64)
 
+IO_BUFFER_DECLARE_TYPE(u128, rb_uint128_t, RB_IO_BUFFER_LITTLE_ENDIAN, rb_uint128_to_numeric, rb_numeric_to_uint128, ruby_swap128_uint)
+IO_BUFFER_DECLARE_TYPE(U128, rb_uint128_t, RB_IO_BUFFER_BIG_ENDIAN, rb_uint128_to_numeric, rb_numeric_to_uint128, ruby_swap128_uint)
+IO_BUFFER_DECLARE_TYPE(s128, rb_int128_t, RB_IO_BUFFER_LITTLE_ENDIAN, rb_int128_to_numeric, rb_numeric_to_int128, ruby_swap128_int)
+IO_BUFFER_DECLARE_TYPE(S128, rb_int128_t, RB_IO_BUFFER_BIG_ENDIAN, rb_int128_to_numeric, rb_numeric_to_int128, ruby_swap128_int)
+
 IO_BUFFER_DECLARE_TYPE(f32, float, RB_IO_BUFFER_LITTLE_ENDIAN, DBL2NUM, NUM2DBL, ruby_swapf32)
 IO_BUFFER_DECLARE_TYPE(F32, float, RB_IO_BUFFER_BIG_ENDIAN, DBL2NUM, NUM2DBL, ruby_swapf32)
 IO_BUFFER_DECLARE_TYPE(f64, double, RB_IO_BUFFER_LITTLE_ENDIAN, DBL2NUM, NUM2DBL, ruby_swapf64)
@@ -1965,6 +2012,10 @@ io_buffer_buffer_type_size(ID buffer_type)
     IO_BUFFER_DATA_TYPE_SIZE(U64)
     IO_BUFFER_DATA_TYPE_SIZE(s64)
     IO_BUFFER_DATA_TYPE_SIZE(S64)
+    IO_BUFFER_DATA_TYPE_SIZE(u128)
+    IO_BUFFER_DATA_TYPE_SIZE(U128)
+    IO_BUFFER_DATA_TYPE_SIZE(s128)
+    IO_BUFFER_DATA_TYPE_SIZE(S128)
     IO_BUFFER_DATA_TYPE_SIZE(f32)
     IO_BUFFER_DATA_TYPE_SIZE(F32)
     IO_BUFFER_DATA_TYPE_SIZE(f64)
@@ -2021,6 +2072,11 @@ rb_io_buffer_get_value(const void* base, size_t size, ID buffer_type, size_t *of
     IO_BUFFER_GET_VALUE(s64)
     IO_BUFFER_GET_VALUE(S64)
 
+    IO_BUFFER_GET_VALUE(u128)
+    IO_BUFFER_GET_VALUE(U128)
+    IO_BUFFER_GET_VALUE(s128)
+    IO_BUFFER_GET_VALUE(S128)
+
     IO_BUFFER_GET_VALUE(f32)
     IO_BUFFER_GET_VALUE(F32)
     IO_BUFFER_GET_VALUE(f64)
@@ -2050,6 +2106,10 @@ rb_io_buffer_get_value(const void* base, size_t size, ID buffer_type, size_t *of
  *  * +:U64+: unsigned integer, 8 bytes, big-endian
  *  * +:s64+: signed integer, 8 bytes, little-endian
  *  * +:S64+: signed integer, 8 bytes, big-endian
+ *  * +:u128+: unsigned integer, 16 bytes, little-endian
+ *  * +:U128+: unsigned integer, 16 bytes, big-endian
+ *  * +:s128+: signed integer, 16 bytes, little-endian
+ *  * +:S128+: signed integer, 16 bytes, big-endian
  *  * +:f32+: float, 4 bytes, little-endian
  *  * +:F32+: float, 4 bytes, big-endian
  *  * +:f64+: double, 8 bytes, little-endian
@@ -2287,6 +2347,11 @@ rb_io_buffer_set_value(const void* base, size_t size, ID buffer_type, size_t *of
     IO_BUFFER_SET_VALUE(s64);
     IO_BUFFER_SET_VALUE(S64);
 
+    IO_BUFFER_SET_VALUE(u128);
+    IO_BUFFER_SET_VALUE(U128);
+    IO_BUFFER_SET_VALUE(s128);
+    IO_BUFFER_SET_VALUE(S128);
+
     IO_BUFFER_SET_VALUE(f32);
     IO_BUFFER_SET_VALUE(F32);
     IO_BUFFER_SET_VALUE(f64);
@@ -3859,6 +3924,11 @@ Init_IO_Buffer(void)
     IO_BUFFER_DEFINE_DATA_TYPE(s64);
     IO_BUFFER_DEFINE_DATA_TYPE(S64);
 
+    IO_BUFFER_DEFINE_DATA_TYPE(u128);
+    IO_BUFFER_DEFINE_DATA_TYPE(U128);
+    IO_BUFFER_DEFINE_DATA_TYPE(s128);
+    IO_BUFFER_DEFINE_DATA_TYPE(S128);
+
     IO_BUFFER_DEFINE_DATA_TYPE(f32);
     IO_BUFFER_DEFINE_DATA_TYPE(F32);
     IO_BUFFER_DEFINE_DATA_TYPE(f64);
diff --git a/numeric.c b/numeric.c
index bc0edd6abe..d9e837644f 100644
--- a/numeric.c
+++ b/numeric.c
@@ -3420,6 +3420,229 @@ rb_num2ull(VALUE val)
 
 #endif  /* HAVE_LONG_LONG */
 
+// Conversion functions for unified 128-bit integer structures,
+// These work with or without native 128-bit integer support.
+
+#ifndef HAVE_UINT128_T
+// Helper function to build 128-bit value from bignum digits (fallback path).
+static inline void
+rb_uint128_from_bignum_digits_fallback(rb_uint128_t *result, BDIGIT *digits, size_t length)
+{
+    // Build the 128-bit value from bignum digits:
+    for (long i = length - 1; i >= 0; i--) {
+        // Shift both low and high parts:
+        uint64_t carry = result->parts.low >> (64 - (SIZEOF_BDIGIT * CHAR_BIT));
+        result->parts.low = (result->parts.low << (SIZEOF_BDIGIT * CHAR_BIT)) | digits[i];
+        result->parts.high = (result->parts.high << (SIZEOF_BDIGIT * CHAR_BIT)) | carry;
+    }
+}
+
+// Helper function to convert absolute value of negative bignum to two's complement.
+// Ruby stores negative bignums as absolute values, so we need to convert to two's complement.
+static inline void
+rb_uint128_twos_complement_negate(rb_uint128_t *value)
+{
+    if (value->parts.low == 0) {
+        value->parts.high = ~value->parts.high + 1;
+    }
+    else {
+        value->parts.low = ~value->parts.low + 1;
+        value->parts.high = ~value->parts.high + (value->parts.low == 0 ? 1 : 0);
+    }
+}
+#endif
+
+rb_uint128_t
+rb_numeric_to_uint128(VALUE x)
+{
+    rb_uint128_t result = {0};
+    if (RB_FIXNUM_P(x)) {
+        long value = RB_FIX2LONG(x);
+        if (value < 0) {
+            rb_raise(rb_eRangeError, "negative integer cannot be converted to unsigned 128-bit integer");
+        }
+#ifdef HAVE_UINT128_T
+        result.value = (uint128_t)value;
+#else
+        result.parts.low = (uint64_t)value;
+        result.parts.high = 0;
+#endif
+        return result;
+    }
+    else if (RB_BIGNUM_TYPE_P(x)) {
+        if (BIGNUM_NEGATIVE_P(x)) {
+            rb_raise(rb_eRangeError, "negative integer cannot be converted to unsigned 128-bit integer");
+        }
+        size_t length = BIGNUM_LEN(x);
+#ifdef HAVE_UINT128_T
+        if (length > roomof(SIZEOF_INT128_T, SIZEOF_BDIGIT)) {
+            rb_raise(rb_eRangeError, "bignum too big to convert into 'unsigned 128-bit integer'");
+        }
+        BDIGIT *digits = BIGNUM_DIGITS(x);
+        result.value = 0;
+        for (long i = length - 1; i >= 0; i--) {
+            result.value = (result.value << (SIZEOF_BDIGIT * CHAR_BIT)) | digits[i];
+        }
+#else
+        // Check if bignum fits in 128 bits (16 bytes)
+        if (length > roomof(16, SIZEOF_BDIGIT)) {
+            rb_raise(rb_eRangeError, "bignum too big to convert into 'unsigned 128-bit integer'");
+        }
+        BDIGIT *digits = BIGNUM_DIGITS(x);
+        rb_uint128_from_bignum_digits_fallback(&result, digits, length);
+#endif
+        return result;
+    }
+    else {
+        rb_raise(rb_eTypeError, "not an integer");
+    }
+}
+
+rb_int128_t
+rb_numeric_to_int128(VALUE x)
+{
+    rb_int128_t result = {0};
+    if (RB_FIXNUM_P(x)) {
+        long value = RB_FIX2LONG(x);
+#ifdef HAVE_UINT128_T
+        result.value = (int128_t)value;
+#else
+        if (value < 0) {
+            // Two's complement representation: for negative values, sign extend
+            // Convert to unsigned: for -1, we want all bits set
+            result.parts.low = (uint64_t)value; // This will be the two's complement representation
+            result.parts.high = UINT64_MAX; // Sign extend: all bits set for negative
+        }
+        else {
+            result.parts.low = (uint64_t)value;
+            result.parts.high = 0;
+        }
+#endif
+        return result;
+    }
+    else if (RB_BIGNUM_TYPE_P(x)) {
+        size_t length = BIGNUM_LEN(x);
+#ifdef HAVE_UINT128_T
+        if (length > roomof(SIZEOF_INT128_T, SIZEOF_BDIGIT)) {
+            rb_raise(rb_eRangeError, "bignum too big to convert into 'signed 128-bit integer'");
+        }
+        BDIGIT *digits = BIGNUM_DIGITS(x);
+        uint128_t unsigned_result = 0;
+        for (long i = length - 1; i >= 0; i--) {
+            unsigned_result = (unsigned_result << (SIZEOF_BDIGIT * CHAR_BIT)) | digits[i];
+        }
+        if (BIGNUM_NEGATIVE_P(x)) {
+            // Convert from two's complement
+            // Maximum negative value is 2^127
+            if (unsigned_result > ((uint128_t)1 << 127)) {
+                rb_raise(rb_eRangeError, "bignum too big to convert into 'signed 128-bit integer'");
+            }
+            result.value = -(int128_t)(unsigned_result - 1) - 1;
+        }
+        else {
+            // Maximum positive value is 2^127 - 1
+            if (unsigned_result > (((uint128_t)1 << 127) - 1)) {
+                rb_raise(rb_eRangeError, "bignum too big to convert into 'signed 128-bit integer'");
+            }
+            result.value = (int128_t)unsigned_result;
+        }
+#else
+        if (length > roomof(16, SIZEOF_BDIGIT)) {
+            rb_raise(rb_eRangeError, "bignum too big to convert into 'signed 128-bit integer'");
+        }
+        BDIGIT *digits = BIGNUM_DIGITS(x);
+        rb_uint128_t unsigned_result = {0};
+        rb_uint128_from_bignum_digits_fallback(&unsigned_result, digits, length);
+        if (BIGNUM_NEGATIVE_P(x)) {
+            // Check if value fits in signed 128-bit (max negative is 2^127)
+            uint64_t max_neg_high = (uint64_t)1 << 63;
+            if (unsigned_result.parts.high > max_neg_high || (unsigned_result.parts.high == max_neg_high && unsigned_result.parts.low > 0)) {
+                rb_raise(rb_eRangeError, "bignum too big to convert into 'signed 128-bit integer'");
+            }
+            // Convert from absolute value to two's complement (Ruby stores negative as absolute value)
+            rb_uint128_twos_complement_negate(&unsigned_result);
+            result.parts.low = unsigned_result.parts.low;
+            result.parts.high = (int64_t)unsigned_result.parts.high; // Sign extend
+        }
+        else {
+            // Check if value fits in signed 128-bit (max positive is 2^127 - 1)
+            // Max positive: high = 0x7FFFFFFFFFFFFFFF, low = 0xFFFFFFFFFFFFFFFF
+            uint64_t max_pos_high = ((uint64_t)1 << 63) - 1;
+            if (unsigned_result.parts.high > max_pos_high) {
+                rb_raise(rb_eRangeError, "bignum too big to convert into 'signed 128-bit integer'");
+            }
+            result.parts.low = unsigned_result.parts.low;
+            result.parts.high = unsigned_result.parts.high;
+        }
+#endif
+        return result;
+    }
+    else {
+        rb_raise(rb_eTypeError, "not an integer");
+    }
+}
+
+VALUE
+rb_uint128_to_numeric(rb_uint128_t n)
+{
+#ifdef HAVE_UINT128_T
+    if (n.value <= (uint128_t)RUBY_FIXNUM_MAX) {
+        return LONG2FIX((long)n.value);
+    }
+    return rb_uint128t2big(n.value);
+#else
+    // If high part is zero and low part fits in fixnum
+    if (n.parts.high == 0 && n.parts.low <= (uint64_t)RUBY_FIXNUM_MAX) {
+        return LONG2FIX((long)n.parts.low);
+    }
+    // Convert to bignum by building it from the two 64-bit parts
+    VALUE bignum = rb_ull2big(n.parts.low);
+    if (n.parts.high > 0) {
+        VALUE high_bignum = rb_ull2big(n.parts.high);
+        // Multiply high part by 2^64 and add to low part
+        VALUE shifted_value = rb_int_lshift(high_bignum, INT2FIX(64));
+        bignum = rb_int_plus(bignum, shifted_value);
+    }
+    return bignum;
+#endif
+}
+
+VALUE
+rb_int128_to_numeric(rb_int128_t n)
+{
+#ifdef HAVE_UINT128_T
+    if (FIXABLE(n.value)) {
+        return LONG2FIX((long)n.value);
+    }
+    return rb_int128t2big(n.value);
+#else
+    int64_t high = (int64_t)n.parts.high;
+    // If it's a small positive value that fits in fixnum
+    if (high == 0 && n.parts.low <= (uint64_t)RUBY_FIXNUM_MAX) {
+        return LONG2FIX((long)n.parts.low);
+    }
+    // Check if it's negative (high bit of high part is set)
+    if (high < 0) {
+        // Negative value - convert from two's complement to absolute value
+        rb_uint128_t unsigned_value = {0};
+        if (n.parts.low == 0) {
+            unsigned_value.parts.low = 0;
+            unsigned_value.parts.high = ~n.parts.high + 1;
+        }
+        else {
+            unsigned_value.parts.low = ~n.parts.low + 1;
+            unsigned_value.parts.high = ~n.parts.high + (unsigned_value.parts.low == 0 ? 1 : 0);
+        }
+        VALUE bignum = rb_uint128_to_numeric(unsigned_value);
+        return rb_int_uminus(bignum);
+    }
+    else {
+        // Positive value
+        return rb_uint128_to_numeric(*(rb_uint128_t*)&n);
+    }
+#endif
+}
+
 /********************************************************************
  *
  * Document-class: Integer
diff --git a/test/ruby/test_io_buffer.rb b/test/ruby/test_io_buffer.rb
index 1e4a6e2fd8..9ff22b4bb3 100644
--- a/test/ruby/test_io_buffer.rb
+++ b/test/ruby/test_io_buffer.rb
@@ -405,6 +405,11 @@ class TestIOBuffer < Test::Unit::TestCase
     :u64 => [0, 2**64-1],
     :s64 => [-2**63, 0, 2**63-1],
 
+    :U128 => [0, 2**64, 2**127-1, 2**128-1],
+    :S128 => [-2**127, -2**63-1, -1, 0, 2**63, 2**127-1],
+    :u128 => [0, 2**64, 2**127-1, 2**128-1],
+    :s128 => [-2**127, -2**63-1, -1, 0, 2**63, 2**127-1],
+
     :F32 => [-1.0, 0.0, 0.5, 1.0, 128.0],
     :F64 => [-1.0, 0.0, 0.5, 1.0, 128.0],
   }
@@ -759,4 +764,146 @@ class TestIOBuffer < Test::Unit::TestCase
 
     assert_predicate buf, :valid?
   end
+
+  def test_128_bit_integers
+    buffer = IO::Buffer.new(32)
+
+    # Test unsigned 128-bit integers
+    test_values_u128 = [
+      0,
+      1,
+      2**64 - 1,
+      2**64,
+      2**127 - 1,
+      2**128 - 1,
+    ]
+
+    test_values_u128.each do |value|
+      buffer.set_value(:u128, 0, value)
+      assert_equal value, buffer.get_value(:u128, 0), "u128: #{value}"
+
+      buffer.set_value(:U128, 0, value)
+      assert_equal value, buffer.get_value(:U128, 0), "U128: #{value}"
+    end
+
+    # Test signed 128-bit integers
+    test_values_s128 = [
+      -2**127,
+      -2**63 - 1,
+      -1,
+      0,
+      1,
+      2**63,
+      2**127 - 1,
+    ]
+
+    test_values_s128.each do |value|
+      buffer.set_value(:s128, 0, value)
+      assert_equal value, buffer.get_value(:s128, 0), "s128: #{value}"
+
+      buffer.set_value(:S128, 0, value)
+      assert_equal value, buffer.get_value(:S128, 0), "S128: #{value}"
+    end
+
+    # Test size_of
+    assert_equal 16, IO::Buffer.size_of(:u128)
+    assert_equal 16, IO::Buffer.size_of(:U128)
+    assert_equal 16, IO::Buffer.size_of(:s128)
+    assert_equal 16, IO::Buffer.size_of(:S128)
+    assert_equal 32, IO::Buffer.size_of([:u128, :u128])
+  end
+
+  def test_integer_endianness_swapping
+    # Test that byte order is swapped correctly for all signed and unsigned integers > 1 byte
+    host_is_le = IO::Buffer::HOST_ENDIAN == IO::Buffer::LITTLE_ENDIAN
+    host_is_be = IO::Buffer::HOST_ENDIAN == IO::Buffer::BIG_ENDIAN
+
+    # Test values that will produce different byte patterns when swapped
+    # Format: [little_endian_type, big_endian_type, test_value, expected_swapped_value]
+    # expected_swapped_value is the result when writing as le_type and reading as be_type
+    # (or vice versa) on a little-endian host
+    test_cases = [
+      [:u16, :U16, 0x1234, 0x3412],
+      [:s16, :S16, 0x1234, 0x3412],
+      [:u32, :U32, 0x12345678, 0x78563412],
+      [:s32, :S32, 0x12345678, 0x78563412],
+      [:u64, :U64, 0x0123456789ABCDEF, 0xEFCDAB8967452301],
+      [:s64, :S64, 0x0123456789ABCDEF, -1167088121787636991],
+      [:u128, :U128, 0x0123456789ABCDEF0123456789ABCDEF, 0xEFCDAB8967452301EFCDAB8967452301],
+      [:u128, :U128, 0x0123456789ABCDEFFEDCBA9876543210, 0x1032547698BADCFEEFCDAB8967452301],
+      [:u128, :U128, 0xFEDCBA98765432100123456789ABCDEF, 0xEFCDAB89674523011032547698BADCFE],
+      [:u128, :U128, 0x123456789ABCDEF0FEDCBA9876543210, 0x1032547698BADCFEF0DEBC9A78563412],
+      [:s128, :S128, 0x0123456789ABCDEF0123456789ABCDEF, -21528975894082904073953971026863512831],
+      [:s128, :S128, 0x0123456789ABCDEFFEDCBA9876543210, 0x1032547698BADCFEEFCDAB8967452301],
+    ]
+
+    test_cases.each do |le_type, be_type, value, expected_swapped|
+      buffer_size = IO::Buffer.size_of(le_type)
+      buffer = IO::Buffer.new(buffer_size * 2)
+
+      # Test little-endian round-trip
+      buffer.set_value(le_type, 0, value)
+      result_le = buffer.get_value(le_type, 0)
+      assert_equal value, result_le, "#{le_type}: round-trip failed"
+
+      # Test big-endian round-trip
+      buffer.set_value(be_type, buffer_size, value)
+      result_be = buffer.get_value(be_type, buffer_size)
+      assert_equal value, result_be, "#{be_type}: round-trip failed"
+
+      # Verify byte patterns are different when endianness differs from host
+      le_bytes = buffer.get_string(0, buffer_size)
+      be_bytes = buffer.get_string(buffer_size, buffer_size)
+
+      if host_is_le
+        # On little-endian host: le_type should match host, be_type should be swapped
+        # So the byte patterns should be different (unless value is symmetric)
+        # Read back with opposite endianness to verify swapping
+        result_le_read_as_be = buffer.get_value(be_type, 0)
+        result_be_read_as_le = buffer.get_value(le_type, buffer_size)
+
+        # The swapped reads should NOT equal the original value (unless it's symmetric)
+        # For most values, this will be different
+        if value != 0 && value != -1 && value.abs != 1
+          refute_equal value, result_le_read_as_be, "#{le_type} written, read as #{be_type} should be swapped on LE host"
+          refute_equal value, result_be_read_as_le, "#{be_type} written, read as #{le_type} should be swapped on LE host"
+        end
+
+        # Verify that reading back with correct endianness works
+        assert_equal value, buffer.get_value(le_type, 0), "#{le_type} should read correctly on LE host"
+        assert_equal value, buffer.get_value(be_type, buffer_size), "#{be_type} should read correctly on LE host (with swapping)"
+      elsif host_is_be
+        # On big-endian host: be_type should match host, le_type should be swapped
+        result_le_read_as_be = buffer.get_value(be_type, 0)
+        result_be_read_as_le = buffer.get_value(le_type, buffer_size)
+
+        # The swapped reads should NOT equal the original value (unless it's symmetric)
+        if value != 0 && value != -1 && value.abs != 1
+          refute_equal value, result_le_read_as_be, "#{le_type} written, read as #{be_type} should be swapped on BE host"
+          refute_equal value, result_be_read_as_le, "#{be_type} written, read as #{le_type} should be swapped on BE host"
+        end
+
+        # Verify that reading back with correct endianness works
+        assert_equal value, buffer.get_value(be_type, buffer_size), "#{be_type} should read correctly on BE host"
+        assert_equal value, buffer.get_value(le_type, 0), "#{le_type} should read correctly on BE host (with swapping)"
+      end
+
+      # Verify that when we write with one endianness and read with the opposite,
+      # we get the expected swapped value
+      buffer.set_value(le_type, 0, value)
+      swapped_value_le_to_be = buffer.get_value(be_type, 0)
+      assert_equal expected_swapped, swapped_value_le_to_be, "#{le_type} written, read as #{be_type} should produce expected swapped value"
+
+      # Also verify the reverse direction
+      buffer.set_value(be_type, buffer_size, value)
+      swapped_value_be_to_le = buffer.get_value(le_type, buffer_size)
+      assert_equal expected_swapped, swapped_value_be_to_le, "#{be_type} written, read as #{le_type} should produce expected swapped value"
+
+      # Verify that writing the swapped value back and reading with original endianness
+      # gives us the original value (double-swap should restore original)
+      buffer.set_value(be_type, 0, swapped_value_le_to_be)
+      round_trip_value = buffer.get_value(le_type, 0)
+      assert_equal value, round_trip_value, "#{le_type}/#{be_type}: double-swap should restore original value"
+    end
+  end
 end