A part of being a great programmer is having your personal code library. With a personal code library I mean a repository of code that you have an intimate knowledge of and that you can reuse quickly. If you are a C programmer, you don't want to reimplement linked lists, trees, various utility functions, macros and algorithms each time you write a new program. Rather you want to take them from your repository, adjust and incorporate in your code.

A good example is the implementation of linked lists in the Linux kernel. Every kernel developer knows it and uses it if necessary. They wouldn't reimplement it. Another example is all the code written by djb. It's so good that people have taken it and turned into libdjb code library.

With this article I'd like to open a new topic in this blog where I share code from my personal code library. I'll start with a C header file that I created just recently based on my Bit Hacks You Should Know About article.

This header file is called "catonmat.net/ftp/bithacks.h" and it contains various macros for bit manipulations. I also wrote tests for all the macros in the "catonmat.net/ftp/bithacks-test.c" program.

The most beautiful part of "bithacks.h" is the "B8" macro that allows to write something like " x = B8(10101010) " and turns it into " x = 170 " (because 10101010 in binary is 170 in decimal). I have not yet added B16 and B32 macros but I will add them when I publish the article on advanced bithacks. The credit for the B8 idea goes to Tom Torfs who was the first to write it.

The "bithacks.h" header provides the following macros:

Please see "catonmat.net/ftp/bithacks-test.c" for many examples of these macros.

For those who don't want to download bithacks.h, here is its content:

/* ** bithacks.h - bit hacks macros. v1.0 ** ** Released under the MIT license. */ #ifndef BITHACKS_H #define BITHACKS_H #define HEXIFY(X) 0x##X##LU #define B8IFY(Y) (((Y&0x0000000FLU)?1:0) + \ ((Y&0x000000F0LU)?2:0) + \ ((Y&0x00000F00LU)?4:0) + \ ((Y&0x0000F000LU)?8:0) + \ ((Y&0x000F0000LU)?16:0) + \ ((Y&0x00F00000LU)?32:0) + \ ((Y&0x0F000000LU)?64:0) + \ ((Y&0xF0000000LU)?128:0)) #define B8(Z) ((unsigned char)B8IFY(HEXIFY(Z))) /* test if x is even */ #define B_EVEN(x) (((x)&1)==0) /* test if x is odd */ #define B_ODD(x) (!B_EVEN((x))) /* test if n-th bit in x is set */ #define B_IS_SET(x, n) (((x) & (1<<(n)))?1:0) /* set n-th bit in x */ #define B_SET(x, n) ((x) |= (1<<(n))) /* unset n-th bit in x */ #define B_UNSET(x, n) ((x) &= ~(1<<(n))) /* toggle n-th bit in x */ #define B_TOGGLE(x, n) ((x) ^= (1<<(n))) /* turn off right-most 1-bit in x */ #define B_TURNOFF_1(x) ((x) &= ((x)-1)) /* isolate right-most 1-bit in x */ #define B_ISOLATE_1(x) ((x) &= (-(x))) /* right-propagate right-most 1-bit in x */ #define B_PROPAGATE_1(x) ((x) |= ((x)-1)) /* isolate right-most 0-bit in x */ #define B_ISOLATE_0(x) ((x) = ~(x) & ((x)+1)) /* turn on right-most 0-bit in x */ #define B_TURNON_0(x) ((x) |= ((x)+1)) /* ** more bit hacks coming as soon as I post ** an article on advanced bit hacks */ #endif

And here are all the tests:

/* ** bithacks-test.c - tests for bithacks.h ** ** Released under the MIT license. */ #include <stdio.h> #include <stdlib.h> #include "bithacks.h" int error_count; #define TEST_OK(exp, what) do { \ if ((exp)!=(what)) { \ error_count++; \ printf("Test '%s' at line %d failed.

", #exp, __LINE__); \ } } while(0) #define TEST_END do { \ if (error_count) { \ printf("Testing failed: %d failed tests.

", error_count); \ } else { \ printf("All tests OK.

"); \ } } while (0) void test_B8() { /* test B8 */ TEST_OK(B8(0), 0); TEST_OK(B8(1), 1); TEST_OK(B8(11), 3); TEST_OK(B8(111), 7); TEST_OK(B8(1111), 15); TEST_OK(B8(11111), 31); TEST_OK(B8(111111), 63); TEST_OK(B8(1111111), 127); TEST_OK(B8(00000000), 0); TEST_OK(B8(11111111), 255); TEST_OK(B8(1010), 10); TEST_OK(B8(10101010), 170); TEST_OK(B8(01010101), 85); } void test_B_EVEN() { /* test B_EVEN */ TEST_OK(B_EVEN(B8(0)), 1); TEST_OK(B_EVEN(B8(00000000)), 1); TEST_OK(B_EVEN(B8(1)), 0); TEST_OK(B_EVEN(B8(11111111)), 0); TEST_OK(B_EVEN(B8(10101010)), 1); TEST_OK(B_EVEN(B8(01010101)), 0); TEST_OK(B_EVEN(44), 1); TEST_OK(B_EVEN(131), 0); } void test_B_ODD() { /* test B_ODD */ TEST_OK(B_ODD(B8(0)), 0); TEST_OK(B_ODD(B8(00000000)), 0); TEST_OK(B_ODD(B8(1)), 1); TEST_OK(B_ODD(B8(11111111)), 1); TEST_OK(B_ODD(B8(10101010)), 0); TEST_OK(B_ODD(B8(01010101)), 1); TEST_OK(B_ODD(44), 0); TEST_OK(B_ODD(131), 1); } void test_B_IS_SET() { /* test B_IS_SET */ TEST_OK(B_IS_SET(B8(0), 0), 0); TEST_OK(B_IS_SET(B8(00000000), 0), 0); TEST_OK(B_IS_SET(B8(1), 0), 1); TEST_OK(B_IS_SET(B8(11111111), 0), 1); TEST_OK(B_IS_SET(B8(11111111), 1), 1); TEST_OK(B_IS_SET(B8(11111111), 2), 1); TEST_OK(B_IS_SET(B8(11111111), 3), 1); TEST_OK(B_IS_SET(B8(11111111), 4), 1); TEST_OK(B_IS_SET(B8(11111111), 5), 1); TEST_OK(B_IS_SET(B8(11111111), 6), 1); TEST_OK(B_IS_SET(B8(11111111), 7), 1); TEST_OK(B_IS_SET(B8(11110000), 0), 0); TEST_OK(B_IS_SET(B8(11110000), 1), 0); TEST_OK(B_IS_SET(B8(11110000), 2), 0); TEST_OK(B_IS_SET(B8(11110000), 3), 0); TEST_OK(B_IS_SET(B8(11110000), 4), 1); TEST_OK(B_IS_SET(B8(11110000), 5), 1); TEST_OK(B_IS_SET(B8(11110000), 6), 1); TEST_OK(B_IS_SET(B8(11110000), 7), 1); TEST_OK(B_IS_SET(B8(00001111), 0), 1); TEST_OK(B_IS_SET(B8(00001111), 1), 1); TEST_OK(B_IS_SET(B8(00001111), 2), 1); TEST_OK(B_IS_SET(B8(00001111), 3), 1); TEST_OK(B_IS_SET(B8(00001111), 4), 0); TEST_OK(B_IS_SET(B8(00001111), 5), 0); TEST_OK(B_IS_SET(B8(00001111), 6), 0); TEST_OK(B_IS_SET(B8(00001111), 7), 0); TEST_OK(B_IS_SET(B8(10101010), 0), 0); TEST_OK(B_IS_SET(B8(10101010), 1), 1); TEST_OK(B_IS_SET(B8(10101010), 2), 0); TEST_OK(B_IS_SET(B8(10101010), 3), 1); TEST_OK(B_IS_SET(B8(10101010), 4), 0); TEST_OK(B_IS_SET(B8(10101010), 5), 1); TEST_OK(B_IS_SET(B8(10101010), 6), 0); TEST_OK(B_IS_SET(B8(10101010), 7), 1); TEST_OK(B_IS_SET(B8(01010101), 0), 1); TEST_OK(B_IS_SET(B8(01010101), 1), 0); TEST_OK(B_IS_SET(B8(01010101), 2), 1); TEST_OK(B_IS_SET(B8(01010101), 3), 0); TEST_OK(B_IS_SET(B8(01010101), 4), 1); TEST_OK(B_IS_SET(B8(01010101), 5), 0); TEST_OK(B_IS_SET(B8(01010101), 6), 1); TEST_OK(B_IS_SET(B8(01010101), 7), 0); } void test_B_SET() { /* test B_SET */ unsigned char x; x = B8(00000000); TEST_OK(B_SET(x, 0), B8(00000001)); TEST_OK(B_SET(x, 1), B8(00000011)); TEST_OK(B_SET(x, 2), B8(00000111)); TEST_OK(B_SET(x, 3), B8(00001111)); TEST_OK(B_SET(x, 4), B8(00011111)); TEST_OK(B_SET(x, 5), B8(00111111)); TEST_OK(B_SET(x, 6), B8(01111111)); TEST_OK(B_SET(x, 7), B8(11111111)); x = B8(11111111); TEST_OK(B_SET(x, 0), B8(11111111)); TEST_OK(B_SET(x, 1), B8(11111111)); TEST_OK(B_SET(x, 2), B8(11111111)); TEST_OK(B_SET(x, 3), B8(11111111)); TEST_OK(B_SET(x, 4), B8(11111111)); TEST_OK(B_SET(x, 5), B8(11111111)); TEST_OK(B_SET(x, 6), B8(11111111)); TEST_OK(B_SET(x, 7), B8(11111111)); } void test_B_UNSET() { unsigned char x; x = B8(11111111); TEST_OK(B_UNSET(x, 0), B8(11111110)); TEST_OK(B_UNSET(x, 1), B8(11111100)); TEST_OK(B_UNSET(x, 2), B8(11111000)); TEST_OK(B_UNSET(x, 3), B8(11110000)); TEST_OK(B_UNSET(x, 4), B8(11100000)); TEST_OK(B_UNSET(x, 5), B8(11000000)); TEST_OK(B_UNSET(x, 6), B8(10000000)); TEST_OK(B_UNSET(x, 7), B8(00000000)); x = B8(00000000); TEST_OK(B_UNSET(x, 0), B8(00000000)); TEST_OK(B_UNSET(x, 1), B8(00000000)); TEST_OK(B_UNSET(x, 2), B8(00000000)); TEST_OK(B_UNSET(x, 3), B8(00000000)); TEST_OK(B_UNSET(x, 4), B8(00000000)); TEST_OK(B_UNSET(x, 5), B8(00000000)); TEST_OK(B_UNSET(x, 6), B8(00000000)); TEST_OK(B_UNSET(x, 7), B8(00000000)); } void test_B_TOGGLE() { unsigned char x = B8(11111111); TEST_OK(B_TOGGLE(x, 0), B8(11111110)); TEST_OK(B_TOGGLE(x, 0), B8(11111111)); TEST_OK(B_TOGGLE(x, 1), B8(11111101)); TEST_OK(B_TOGGLE(x, 1), B8(11111111)); TEST_OK(B_TOGGLE(x, 2), B8(11111011)); TEST_OK(B_TOGGLE(x, 2), B8(11111111)); TEST_OK(B_TOGGLE(x, 3), B8(11110111)); TEST_OK(B_TOGGLE(x, 3), B8(11111111)); TEST_OK(B_TOGGLE(x, 4), B8(11101111)); TEST_OK(B_TOGGLE(x, 4), B8(11111111)); TEST_OK(B_TOGGLE(x, 5), B8(11011111)); TEST_OK(B_TOGGLE(x, 5), B8(11111111)); TEST_OK(B_TOGGLE(x, 6), B8(10111111)); TEST_OK(B_TOGGLE(x, 6), B8(11111111)); TEST_OK(B_TOGGLE(x, 7), B8(01111111)); TEST_OK(B_TOGGLE(x, 7), B8(11111111)); } void test_B_TURNOFF_1() { unsigned char x; x = B8(11111111); TEST_OK(B_TURNOFF_1(x), B8(11111110)); TEST_OK(B_TURNOFF_1(x), B8(11111100)); TEST_OK(B_TURNOFF_1(x), B8(11111000)); TEST_OK(B_TURNOFF_1(x), B8(11110000)); TEST_OK(B_TURNOFF_1(x), B8(11100000)); TEST_OK(B_TURNOFF_1(x), B8(11000000)); TEST_OK(B_TURNOFF_1(x), B8(10000000)); TEST_OK(B_TURNOFF_1(x), B8(00000000)); TEST_OK(B_TURNOFF_1(x), B8(00000000)); x = B8(10101010); TEST_OK(B_TURNOFF_1(x), B8(10101000)); TEST_OK(B_TURNOFF_1(x), B8(10100000)); TEST_OK(B_TURNOFF_1(x), B8(10000000)); TEST_OK(B_TURNOFF_1(x), B8(00000000)); TEST_OK(B_TURNOFF_1(x), B8(00000000)); x = B8(01010101); TEST_OK(B_TURNOFF_1(x), B8(01010100)); TEST_OK(B_TURNOFF_1(x), B8(01010000)); TEST_OK(B_TURNOFF_1(x), B8(01000000)); TEST_OK(B_TURNOFF_1(x), B8(00000000)); TEST_OK(B_TURNOFF_1(x), B8(00000000)); } void test_B_ISOLATE_1() { unsigned char x; x = B8(11111111); TEST_OK(B_ISOLATE_1(x), B8(00000001)); TEST_OK(B_ISOLATE_1(x), B8(00000001)); x = B8(11111110); TEST_OK(B_ISOLATE_1(x), B8(00000010)); TEST_OK(B_ISOLATE_1(x), B8(00000010)); x = B8(11111100); TEST_OK(B_ISOLATE_1(x), B8(00000100)); TEST_OK(B_ISOLATE_1(x), B8(00000100)); x = B8(11111000); TEST_OK(B_ISOLATE_1(x), B8(00001000)); TEST_OK(B_ISOLATE_1(x), B8(00001000)); x = B8(11110000); TEST_OK(B_ISOLATE_1(x), B8(00010000)); TEST_OK(B_ISOLATE_1(x), B8(00010000)); x = B8(11100000); TEST_OK(B_ISOLATE_1(x), B8(00100000)); TEST_OK(B_ISOLATE_1(x), B8(00100000)); x = B8(11000000); TEST_OK(B_ISOLATE_1(x), B8(01000000)); TEST_OK(B_ISOLATE_1(x), B8(01000000)); x = B8(10000000); TEST_OK(B_ISOLATE_1(x), B8(10000000)); TEST_OK(B_ISOLATE_1(x), B8(10000000)); x = B8(00000000); TEST_OK(B_ISOLATE_1(x), B8(00000000)); x = B8(10000000); TEST_OK(B_ISOLATE_1(x), B8(10000000)); x = B8(10001001); TEST_OK(B_ISOLATE_1(x), B8(00000001)); x = B8(10001000); TEST_OK(B_ISOLATE_1(x), B8(00001000)); } void test_B_PROPAGATE_1() { unsigned char x; x = B8(00000000); TEST_OK(B_PROPAGATE_1(x), B8(11111111)); TEST_OK(B_PROPAGATE_1(x), B8(11111111)); x = B8(10000000); TEST_OK(B_PROPAGATE_1(x), B8(11111111)); x = B8(11000000); TEST_OK(B_PROPAGATE_1(x), B8(11111111)); x = B8(11100000); TEST_OK(B_PROPAGATE_1(x), B8(11111111)); x = B8(11110000); TEST_OK(B_PROPAGATE_1(x), B8(11111111)); x = B8(11111000); TEST_OK(B_PROPAGATE_1(x), B8(11111111)); x = B8(11111100); TEST_OK(B_PROPAGATE_1(x), B8(11111111)); x = B8(11111110); TEST_OK(B_PROPAGATE_1(x), B8(11111111)); x = B8(11111111); TEST_OK(B_PROPAGATE_1(x), B8(11111111)); x = B8(00100000); TEST_OK(B_PROPAGATE_1(x), B8(00111111)); TEST_OK(B_PROPAGATE_1(x), B8(00111111)); x = B8(10101000); TEST_OK(B_PROPAGATE_1(x), B8(10101111)); TEST_OK(B_PROPAGATE_1(x), B8(10101111)); x = B8(10101010); TEST_OK(B_PROPAGATE_1(x), B8(10101011)); TEST_OK(B_PROPAGATE_1(x), B8(10101011)); x = B8(10101010); TEST_OK(B_PROPAGATE_1(x), B8(10101011)); TEST_OK(B_PROPAGATE_1(x), B8(10101011)); } void test_B_ISOLATE_0() { unsigned char x; x = B8(00000000); TEST_OK(B_ISOLATE_0(x), B8(00000001)); TEST_OK(B_ISOLATE_0(x), B8(00000010)); TEST_OK(B_ISOLATE_0(x), B8(00000001)); x = B8(00000011); TEST_OK(B_ISOLATE_0(x), B8(00000100)); TEST_OK(B_ISOLATE_0(x), B8(00000001)); x = B8(00000111); TEST_OK(B_ISOLATE_0(x), B8(00001000)); TEST_OK(B_ISOLATE_0(x), B8(00000001)); x = B8(00001111); TEST_OK(B_ISOLATE_0(x), B8(00010000)); TEST_OK(B_ISOLATE_0(x), B8(00000001)); x = B8(00011111); TEST_OK(B_ISOLATE_0(x), B8(00100000)); TEST_OK(B_ISOLATE_0(x), B8(00000001)); x = B8(00111111); TEST_OK(B_ISOLATE_0(x), B8(01000000)); TEST_OK(B_ISOLATE_0(x), B8(00000001)); x = B8(01111111); TEST_OK(B_ISOLATE_0(x), B8(10000000)); TEST_OK(B_ISOLATE_0(x), B8(00000001)); x = B8(11111111); TEST_OK(B_ISOLATE_0(x), B8(00000000)); x = B8(01010101); TEST_OK(B_ISOLATE_0(x), B8(00000010)); x = B8(01010111); TEST_OK(B_ISOLATE_0(x), B8(00001000)); x = B8(01011111); TEST_OK(B_ISOLATE_0(x), B8(00100000)); x = B8(01111111); TEST_OK(B_ISOLATE_0(x), B8(10000000)); } void test_B_TURNON_0() { unsigned char x; x = B8(00000000); TEST_OK(B_TURNON_0(x), B8(00000001)); TEST_OK(B_TURNON_0(x), B8(00000011)); TEST_OK(B_TURNON_0(x), B8(00000111)); TEST_OK(B_TURNON_0(x), B8(00001111)); TEST_OK(B_TURNON_0(x), B8(00011111)); TEST_OK(B_TURNON_0(x), B8(00111111)); TEST_OK(B_TURNON_0(x), B8(01111111)); TEST_OK(B_TURNON_0(x), B8(11111111)); TEST_OK(B_TURNON_0(x), B8(11111111)); x = B8(10101010); TEST_OK(B_TURNON_0(x), B8(10101011)); TEST_OK(B_TURNON_0(x), B8(10101111)); TEST_OK(B_TURNON_0(x), B8(10111111)); TEST_OK(B_TURNON_0(x), B8(11111111)); x = B8(10000000); TEST_OK(B_TURNON_0(x), B8(10000001)); TEST_OK(B_TURNON_0(x), B8(10000011)); TEST_OK(B_TURNON_0(x), B8(10000111)); TEST_OK(B_TURNON_0(x), B8(10001111)); TEST_OK(B_TURNON_0(x), B8(10011111)); TEST_OK(B_TURNON_0(x), B8(10111111)); TEST_OK(B_TURNON_0(x), B8(11111111)); } int main() { test_B8(); test_B_EVEN(); test_B_ODD(); test_B_IS_SET(); test_B_SET(); test_B_UNSET(); test_B_TOGGLE(); test_B_TURNOFF_1(); test_B_ISOLATE_1(); test_B_PROPAGATE_1(); test_B_ISOLATE_0(); test_B_TURNON_0(); TEST_END; return error_count ? EXIT_FAILURE : EXIT_SUCCESS; }

Download bithacks.h header file

The next post about this topic will be on advanced bithacks and extending bithacks.h with these new, advanced bithacks. See you then!