diff --git a/examples/CMakeLists.txt b/examples/CMakeLists.txt
index d5c0bb9d..bfc718ee 100644
--- a/examples/CMakeLists.txt
+++ b/examples/CMakeLists.txt
@@ -30,6 +30,7 @@ add_subdirectory(levenshtein)
 add_subdirectory(list)
 add_subdirectory(log)
 add_subdirectory(log2)
+add_subdirectory(math)
 add_subdirectory(matrix)
 add_subdirectory(mpi)
 add_subdirectory(notifier)
diff --git a/examples/math/.gitignore b/examples/math/.gitignore
new file mode 100644
index 00000000..cadac6b5
--- /dev/null
+++ b/examples/math/.gitignore
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+/math-abs
diff --git a/examples/math/CMakeLists.txt b/examples/math/CMakeLists.txt
new file mode 100644
index 00000000..14e6e329
--- /dev/null
+++ b/examples/math/CMakeLists.txt
@@ -0,0 +1,22 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+#
+# Copyright(c) 2023 ffashion <helloworldffashion@gmail.com>
+#
+
+add_executable(math-abs abs.c)
+target_link_libraries(math-abs bfdev)
+add_test(math-abs math-abs)
+
+if(${CMAKE_PROJECT_NAME} STREQUAL "bfdev")
+    install(FILES
+        abs.c
+        DESTINATION
+        ${CMAKE_INSTALL_DOCDIR}/examples/list
+    )
+
+    install(TARGETS
+        math-abs
+        DESTINATION
+        ${CMAKE_INSTALL_DOCDIR}/bin
+    )
+endif()
diff --git a/examples/math/abs.c b/examples/math/abs.c
new file mode 100644
index 00000000..e334fbc0
--- /dev/null
+++ b/examples/math/abs.c
@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: LGPL-3.0-or-later */
+/*
+ * Copyright(c) 2024 John Sanpe <sanpeqf@gmail.com>
+ */
+
+#define MODULE_NAME "math-abs"
+#define bfdev_log_fmt(fmt) MODULE_NAME ": " fmt
+
+#include <bfdev/log.h>
+#include <bfdev/math.h>
+#include <bfdev/limits.h>
+
+#define ABS_TEST(name, min, max) ({         \
+    long long __result;                     \
+    __result = (long long)bfdev_abs(min);   \
+    bfdev_log_info(name " %lld -> %lld\n",  \
+        (long long)min, __result);          \
+    if (max != __result) {                  \
+        bfdev_log_err("test failed");       \
+        return 1;                           \
+    }                                       \
+})
+
+int
+main(int argc, const char *argv[])
+{
+    ABS_TEST("char", BFDEV_CHAR_MIN + 1, BFDEV_CHAR_MAX);
+    ABS_TEST("short", BFDEV_SHRT_MIN + 1, BFDEV_SHRT_MAX);
+    ABS_TEST("int", BFDEV_INT_MIN + 1, BFDEV_INT_MAX);
+    ABS_TEST("long", BFDEV_LONG_MIN + 1, BFDEV_LONG_MAX);
+    ABS_TEST("long long", BFDEV_LLONG_MIN + 1, BFDEV_LLONG_MAX);
+
+    return 0;
+}
diff --git a/include/bfdev/math.h b/include/bfdev/math.h
index 36f17250..8de107cf 100644
--- a/include/bfdev/math.h
+++ b/include/bfdev/math.h
@@ -38,6 +38,79 @@ BFDEV_BEGIN_DECLS
     (x) & ~bfdev_round_mask(x, y) \
 )
 
+#define bfdev_abs_expr(var, type, other) __builtin_choose_expr( \
+    __builtin_types_compatible_p(typeof(var), signed type) ||   \
+    __builtin_types_compatible_p(typeof(var), unsigned type),   \
+    ({                                                          \
+        signed type __var;                                      \
+        __var = (signed type)(var);                             \
+        __var < 0 ? - __var : __var;                            \
+    }), other                                                   \
+)
+
+/**
+ * bfdev_abs - return absolute value of an argument.
+ *
+ * If it is unsigned type, it is converted to signed type first.
+ * char is treated as if it was signed but the macro's
+ * return type is preserved as char.
+ */
+#define bfdev_abs(var)                          \
+    bfdev_abs_expr(var, long long,              \
+    bfdev_abs_expr(var, long,                   \
+    bfdev_abs_expr(var, int,                    \
+    bfdev_abs_expr(var, short,                  \
+    bfdev_abs_expr(var, char,                   \
+        __builtin_choose_expr(                  \
+        __builtin_types_compatible_p(           \
+            typeof(var), char),                 \
+            (char) ({                           \
+                signed char __var;              \
+                __var = (signed char)(var);     \
+                __var < 0 ? - __var : __var;    \
+            }),                                 \
+            ((void)0)                           \
+        )                                       \
+    ))))                                        \
+)
+
+/**
+ * bfdev_abs_diff - return absolute value of the difference between the args.
+ * @var1: the first argument.
+ * @var2: the second argument.
+ */
+#define bfdev_abs_diff(var1, var2) ({   \
+	typeof(var1) __var1, __var2;        \
+                                        \
+    __var1 = (typeof(var1))(var1);      \
+    __var2 = (typeof(var1))(var2);      \
+                                        \
+	__var1 > __var2                     \
+        ? (__var1 - __var2)             \
+        : (__var2 - __var1);	        \
+})
+
+/**
+ * BFDEV_MULT_FRAC
+ *
+ * Calculate "value * numer / denom"
+ * without unnecessary overflow or loss of precision.
+ */
+#define BFDEV_MULT_FRAC(value, numer, denom) ({ \
+    typeof(value) __value, __numer, __denom;    \
+    typeof(value) __quot, __rem;                \
+                                                \
+    __value = (typeof(value))(value);           \
+    __numer = (typeof(value))(numer);           \
+    __denom = (typeof(value))(denom);           \
+                                                \
+    __quot = (__value) / (__denom);             \
+    __rem = (__value) % (__denom);              \
+                                                \
+    (__quot * (__numer)) +                      \
+        ((__rem * (__numer)) / (__denom));      \
+})
+
 /**
  * BFDEV_DIV_ROUND_UP - round up division.
  * @n: divisor number.