Refactor overflow

examples/CMakeLists.txt

@@ -35,6 +35,7 @@ add_subdirectory(matrix)
 add_subdirectory(mpi)
 add_subdirectory(notifier)
 add_subdirectory(once)
+add_subdirectory(overflow)
 add_subdirectory(prandom)
 add_subdirectory(radix)
 add_subdirectory(ratelimit)

examples/overflow/.gitignore

@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+/overflow-simple

examples/overflow/CMakeLists.txt

@@ -0,0 +1,22 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+#
+# Copyright(c) 2023 ffashion <helloworldffashion@gmail.com>
+#
+
+add_executable(overflow-simple simple.c)
+target_link_libraries(overflow-simple bfdev)
+add_test(overflow-simple overflow-simple)
+
+if(${CMAKE_PROJECT_NAME} STREQUAL "bfdev")
+    install(FILES
+        simple.c
+        DESTINATION
+        ${CMAKE_INSTALL_DOCDIR}/examples/overflow
+    )
+
+    install(TARGETS
+        overflow-simple
+        DESTINATION
+        ${CMAKE_INSTALL_DOCDIR}/bin
+    )
+endif()

examples/overflow/simple.c

@@ -0,0 +1,28 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright(c) 2023 John Sanpe <sanpeqf@gmail.com>
+ */
+
+#define MODULE_NAME "overflow-simple"
+#define bfdev_log_fmt(fmt) MODULE_NAME ": " fmt
+
+#include <bfdev/log.h>
+#include <bfdev/overflow.h>
+
+int
+main(int argc, const char *argv[])
+{
+    bfdev_log_info("(signed char)127 + 1 = %d\n",
+        bfdev_overflow_add((signed char)127, 1));
+
+    bfdev_log_info("(unsigned char)255 + 1 = %d\n",
+        bfdev_overflow_add((unsigned char)255, 1));
+
+    bfdev_log_info("(signed char)-128 - 1 = %d\n",
+        bfdev_overflow_sub((signed char)-128, 1));
+
+    bfdev_log_info("(unsigned char)0 - 1 = %d\n",
+        bfdev_overflow_sub((unsigned char)0, 1));
+
+    return 0;
+}

include/bfdev/compiler.h

@@ -38,6 +38,15 @@ BFDEV_BEGIN_DECLS
 #define bfdev_is_signed(type) (((type)(-1)) < (type)1)
 #define bfdev_is_unsigned(type) (!bfdev_is_signed(type))
 
+#define bfdev_type_half_max(type) \
+    ((type)1 << (8 * sizeof(type) - 1 - bfdev_is_signed(type)))
+
+#define bfdev_type_max(type) \
+    ((type)((bfdev_type_half_max(type) - 1) + bfdev_type_half_max(type)))
+
+#define bfdev_type_min(type) \
+    (((type)((type)-bfdev_type_max(type) - (type)1)))
+
 /* Not-quite-unique ID. */
 #ifndef __BFDEV_UNIQUE_ID
 # define __BFDEV_UNIQUE_ID(prefix) __BFDEV_PASTE(__BFDEV_PASTE(__UNIQUE_ID_, prefix), __LINE__)

include/bfdev/overflow.h

@@ -9,6 +9,7 @@
 #include <bfdev/config.h>
 #include <bfdev/types.h>
 #include <bfdev/stddef.h>
+#include <bfdev/limits.h>
 
 BFDEV_BEGIN_DECLS
 
@@ -18,7 +19,7 @@ BFDEV_BEGIN_DECLS
  * @b: second addend.
  * @d: pointer to store sum.
  *
- * Returns 0 on success.
+ * Returns true on wrap-around, false otherwise.
  */
 #define bfdev_overflow_check_add(a, b, d)       \
 bfdev_overflow_check(({                         \
@@ -36,7 +37,7 @@ bfdev_overflow_check(({                         \
  * @b: subtrahend; value to subtract from @a.
  * @d: pointer to store difference.
  *
- * Returns 0 on success.
+ * Returns true on wrap-around, false otherwise.
  */
 #define bfdev_overflow_check_sub(a, b, d)       \
 bfdev_overflow_check(({                         \
@@ -54,7 +55,7 @@ bfdev_overflow_check(({                         \
  * @b: second factor.
  * @d: pointer to store product.
  *
- * Returns 0 on success.
+ * Returns true on wrap-around, false otherwise.
  */
 #define bfdev_overflow_check_mul(a, b, d)       \
 bfdev_overflow_check(({                         \
@@ -71,23 +72,23 @@ bfdev_overflow_check(({                         \
     type __b = (type)(b);                       \
     type __d;                                   \
     bfdev_overflow_check_add(__a, __b, &__d)    \
-    ? (type)~0ULL : __d;                        \
+    ? bfdev_type_max(type) : __d;               \
 })
 
 #define bfdev_overflow_sub_type(type, a, b) ({  \
     type __a = (type)(a);                       \
     type __b = (type)(b);                       \
     type __d;                                   \
     bfdev_overflow_check_sub(__a, __b, &__d)    \
-    ? (type)~0ULL : __d;                        \
+    ? bfdev_type_min(type) : __d;               \
 })
 
 #define bfdev_overflow_mul_type(type, a, b) ({  \
     type __a = (type)(a);                       \
     type __b = (type)(b);                       \
     type __d;                                   \
     bfdev_overflow_check_mul(__a, __b, &__d)    \
-    ? (type)~0ULL : __d;                        \
+    ? bfdev_type_max(type) : __d;               \
 })
 
 static inline __bfdev_must_check bfdev_bool
@@ -101,7 +102,8 @@ bfdev_overflow_check(bfdev_bool overflow)
  * @a: first addend.
  * @b: second addend.
  *
- * Returns (type)~0ULL on failed.
+ * Returns: calculate @a + @b, any overflow causing the
+ * return value to be bfdev_type_max(type).
  */
 #define bfdev_overflow_add(a, b) \
     bfdev_overflow_add_type(typeof(a), a, b)
@@ -111,7 +113,8 @@ bfdev_overflow_check(bfdev_bool overflow)
  * @a: minuend; value to subtract from.
  * @b: subtrahend; value to subtract from @a.
  *
- * Returns (type)~0ULL on failed.
+ * Returns: calculate @a - @b, any overflow causing the
+ * return value to be bfdev_type_min(type).
  */
 #define bfdev_overflow_sub(a, b) \
     bfdev_overflow_sub_type(typeof(a), a, b)
@@ -121,7 +124,8 @@ bfdev_overflow_check(bfdev_bool overflow)
  * @a: first factor.
  * @b: second factor.
  *
- * Returns (type)~0ULL on failed.
+ * Returns: calculate @a * @b, any overflow causing the
+ * return value to be bfdev_type_max(type).
  */
 #define bfdev_overflow_mul(a, b) \
     bfdev_overflow_mul_type(typeof(a), a, b)

testsuite/CMakeLists.txt

@@ -15,4 +15,5 @@ add_subdirectory(libc)
 add_subdirectory(list)
 add_subdirectory(memalloc)
 add_subdirectory(mpi)
+add_subdirectory(overflow)
 add_subdirectory(slist)

testsuite/overflow/.gitignore

@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+/overflow-selftest

testsuite/overflow/CMakeLists.txt

@@ -0,0 +1,16 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+#
+# Copyright(c) 2025 John Sanpe <sanpeqf@gmail.com>
+#
+
+add_executable(overflow-selftest selftest.c)
+target_link_libraries(overflow-selftest bfdev testsuite)
+add_test(overflow-selftest overflow-selftest)
+
+if(${CMAKE_PROJECT_NAME} STREQUAL "bfdev")
+    install(TARGETS
+        overflow-selftest
+        DESTINATION
+        ${CMAKE_INSTALL_DOCDIR}/testsuite
+    )
+endif()

testsuite/overflow/selftest.c

@@ -0,0 +1,59 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright(c) 2023 John Sanpe <sanpeqf@gmail.com>
+ */
+
+#define MODULE_NAME "overflow-simple"
+#define bfdev_log_fmt(fmt) MODULE_NAME ": " fmt
+
+#include <stddef.h>
+#include <limits.h>
+#include <stdbool.h>
+#include <bfdev/log.h>
+#include <bfdev/overflow.h>
+#include <testsuite.h>
+
+#define TEST(calculate, limit) ({ \
+    bool cond; \
+    cond = bfdev_overflow_##calculate((limit), 1) == (limit); \
+    if (!cond) \
+        failed = true; \
+    cond ? "okay" : "failed"; \
+})
+
+TESTSUITE(
+    "overflow:selftest", NULL, NULL,
+    "overflow selftest"
+) {
+    bool failed;
+
+    failed = false;
+    bfdev_log_info("add char: %s\n", TEST(add, (signed char)SCHAR_MAX));
+    bfdev_log_info("add short: %s\n", TEST(add, (signed short)SHRT_MAX));
+    bfdev_log_info("add int: %s\n", TEST(add, (signed int)INT_MAX));
+    bfdev_log_info("add long: %s\n", TEST(add, (signed long)LONG_MAX));
+    bfdev_log_info("add long long: %s\n", TEST(add, (signed long long)LLONG_MAX));
+
+    bfdev_log_info("add unsigned char: %s\n", TEST(add, (unsigned char)UCHAR_MAX));
+    bfdev_log_info("add unsigned short: %s\n", TEST(add, (unsigned short)USHRT_MAX));
+    bfdev_log_info("add unsigned int: %s\n", TEST(add, (unsigned int)UINT_MAX));
+    bfdev_log_info("add unsigned long: %s\n", TEST(add, (unsigned long)ULONG_MAX));
+    bfdev_log_info("add unsigned long long: %s\n", TEST(add, (unsigned long long)ULLONG_MAX));
+
+    bfdev_log_info("sub char: %s\n", TEST(sub, (signed char)SCHAR_MIN));
+    bfdev_log_info("sub short: %s\n", TEST(sub, (signed short)SHRT_MIN));
+    bfdev_log_info("sub int: %s\n", TEST(sub, (signed int)INT_MIN));
+    bfdev_log_info("sub long: %s\n", TEST(sub, (signed long)LONG_MIN));
+    bfdev_log_info("sub long long: %s\n", TEST(sub, (signed long long)LLONG_MIN));
+
+    bfdev_log_info("sub unsigned char: %s\n", TEST(sub, (unsigned char)0));
+    bfdev_log_info("sub unsigned short: %s\n", TEST(sub, (unsigned short)0));
+    bfdev_log_info("sub unsigned int: %s\n", TEST(sub, (unsigned int)0));
+    bfdev_log_info("sub unsigned long: %s\n", TEST(sub, (unsigned long)0));
+    bfdev_log_info("sub unsigned long long: %s\n", TEST(sub, (unsigned long long)0));
+
+    if (failed)
+        return -BFDEV_EFAULT;
+
+    return -BFDEV_ENOERR;
+}