Mask Shifting

1C :2void binary_print(unsigned int value) {3unsigned int mask = 0xff000000;4unsigned int shift = 256256256; // or 0x10000005unsigned int byte, byte_iterator, bit_iterator;6for(byte_iterator=0; byte_iterator < 4; byte_iterator++) {7byte = (value & mask) / shift;8printf(" ");9for(bit_iterator=0; bit_iterator < 8; bit_iterator++) {10if(byte & 0x80)11printf("1");12else13printf("0");14byte = 2;15}16mask /= 256;17shift /= 256;18}19}20================================================================21What does it do?22✅ Prints the binary of a 32-bit integer cleanly, byte-by-byte, bit-by-bit.23✅ Used to understand flags, memory layouts, and exploit development. ⚙️24Real Example: `O_WRONLY | O_APPEND | O_CREAT`25In Linux:26C:27define O_WRONLY 0128define O_APPEND 0200029define O_CREAT 010030---------------------------------------------------------------------------------------------------------31Step 1: Calculate Combined Value32O_WRONLY = 0x00000001 = 133O_APPEND = 0x00000800 = 204834O_CREAT = 0x00000100 = 25635Total value = 1 + 2048 + 256 = 2305 (decimal)36-------------------------------------------------------------------------------------------------------37🚀 Step 2: Binary of 230538Decimal: `2305`3932-bit binary:4000000000 00000000 00001000 00000001410x0801` in hex.42--------------------------------------------------------------------------------------------------------43Step 3: Full `binary_print` execution44Initialization:45mask = 0xff000000; // 11111111 00000000 00000000 0000000046shift = 0x1000000; // 1677721647---------------------------------------------------------------------------------------------------------48================================================================49Iteration Table and Detailed Breakdown :50![..](https://cms.ocic.me/api/media/file/Screenshot%20From%202026-06-13%2005-23-17.png)51Detailed Step-by-Step Execution :521. Iteration 1 (byte_iterator = 0)53 Mask:540xFF000000 = 11111111 00000000 00000000 0000000055 Shift:560x01000000 = 1677721657 value & mask:5800000000 00000000 00001000 00000001 &5911111111 00000000 00000000 00000000 =6000000000 00000000 00000000 0000000061 Divide:620 / 16777216 = 063 Bit printing:64Using:65for(bit_iterator=0; bit_iterator < 8; bit_iterator++) {66if(byte & 0x80) printf("1"); else printf("0");67byte *= 2;68}69Since byte = 0:700000000071 Mask and shift update:72mask /= 256 => 0x00FF000073shift /= 256 => 0x00010000 (65536)74================================================================752. Iteration 2 (byte_iterator = 1)76 Mask:770x00FF0000 = 00000000 11111111 00000000 0000000078 Shift:790x00010000 = 6553680 value & mask:8100000000 00000000 00001000 00000001 &8200000000 11111111 00000000 00000000 =8300000000 00000000 00000000 0000000084 Divide:850 / 65536 = 086 Bit printing:870000000088 Mask and shift update:89mask /= 256 => 0x0000FF0090shift /= 256 => 0x00000100 (256)91================================================================923. Iteration 3 (byte_iterator = 2)93 Mask:940x0000FF00 = 00000000 00000000 11111111 0000000095 Shift:960x00000100 = 25697 value & mask:9800000000 00000000 00001000 00000001 &9900000000 00000000 11111111 00000000 =10000000000 00000000 00001000 00000000101 Hex: 0x00000800 = 2048102 Divide:1032048 / 256 = 8104 Bit printing:1058 in binary:10600001000107Printing:108 byte = 8 = 00001000109 loop:110o 00001000 & 0x80 (128) = 0 → 0111o shift left: 00010000112o 00010000 & 0x80 = 0 → 0113o shift: 00100000114o 00100000 & 0x80 = 0 → 0115o shift: 01000000116o 01000000 & 0x80 = 0 → 0117o shift: 10000000118o 10000000 & 0x80 = 128 → 1119o shift: 00000000120o 00000000 & 0x80 = 0 → 0121o repeat → 0122o repeat → 012300001000124 Mask and shift update:125mask /= 256 => 0x000000FF126shift /= 256 => 0x00000001 (1)127================================================================1284. Iteration 4 (byte_iterator = 3)129 Mask:1300x000000FF = 00000000 00000000 00000000 11111111131 Shift:1320x00000001 = 1133 value & mask:13400000000 00000000 00001000 00000001 &13500000000 00000000 00000000 11111111 =13600000000 00000000 00000000 00000001137 Hex: 0x00000001 = 1138 Divide:1391 / 1 = 1140 Bit printing:1411 in binary:14200000001143Printing:144 byte = 1 = 00000001145 loop:146o 00000001 & 0x80 = 0 → 0147o shift: 00000010148o 00000010 & 0x80 = 0 → 0149o shift: 00000100150o 00000100 & 0x80 = 0 → 0151o shift: 00001000152o 00001000 & 0x80 = 0 → 0153o shift: 00010000154o 00010000 & 0x80 = 0 → 0155o shift: 00100000156o 00100000 & 0x80 = 0 → 0157o shift: 01000000158o 01000000 & 0x80 = 0 → 0159o shift: 10000000160o 10000000 & 0x80 = 128 → 116100000001162-------------------------------------------------------------------------------------------------------163Final output:16400000000 00000000 00001000 00000001165Cleanly prints the full 32-bit value of flags, byte-by-byte.166================================================================167Summary :1681. Masking isolates only one byte by zeroing others:169 value & mask1702. Shifting brings the target byte to LSB for easy printing:171 (value & mask) / shift1723. Bit loop (byte & 0x80, then byte *= 2) prints each bit in the isolated byte.1734. Full loop prints 32 bits cleanly, 8 bits per iteration.1745. This logic and muscle memory are critical in reversing and exploitation.175================================================176Why not print value directly?177Directly printing:1782305 = 00000000 00000000 00001000 00000001179is possible, but:180✅ This function:1811. Cleanly separates bytes.1822. Allows bit-by-bit inspection.1833. Is useful for fuzzing, patching, reversing, binary debugging.1844. Builds muscle memory for bit masking and shifting, critical for:1855. Analyzing binary flags186================================================================187🚩 Why Masking and Shifting?1881. Masking: Zeros out unwanted bits, isolates specific byte:189`value & mask` ⇒ Only keeps the target byte.1902. Shifting: Moves isolated byte to least significant position for bit testing:191Allows simple `if (byte & 0x80)` checks for each bit.1923.Bitwise Inspection:193Validate exact flag bits.194Debug system calls, syscall flags, network flags.