Chastity White Rose

Tag: binary

  • New C test program for chastelib

    In my last post, I showed the test program for the Rust version of chastelib. I decided it would make sense to design a similar test program that uses the original C version of the library that I used when converting to Rust. Personally I like this version better. Global variables makes the code cleaner in my opinion because otherwise how would I choose which order the arguments to the functions would go in? This way, the radix and width of the integer string are set by global data before calling the putint function.

    Also notice that the b variable is set to an integer by a string using strint. This is only to demonstrate proper use of the function. Normally it would not be used unless getting string input from a user by command line argument such as was done in chastehex.

    In any case, this library controls all the integer and string conversion so that I can use it in larger projects. Because it is in ANSI C, it is portable to any machine that exists in modern times.

    main.c

    #include <stdio.h>
#include <stdlib.h>
#include "chastelib.h"

int main(int argc, char *argv[])
{
 int a=0,b;

 radix=16;
 int_width=1;

 putstring("This is the official test program for the C version of chastelib.\n");
 b=strint("100");

 putstring("Hello World!\n");
 
 while(a<b)
 {
  radix=2;
  int_width=8;
  putint(a);
  putstring(" ");
  radix=16;
  int_width=2;
  putint(a);
  putstring(" ");
  radix=10;
  int_width=3;
  putint(a);

  if(a>=0x20 && a<=0x7E)
  {
   putstring(" ");
   putchar(a);
  }

  putstring("\n");
  a+=1;
 }
  
 return 0;
}

    Below is the command to compile and run it and the output.

    gcc -Wall -ansi -pedantic main.c -o main && ./main
This is the official test program for the C version of chastelib.
Hello World!
00000000 00 000
00000001 01 001
00000010 02 002
00000011 03 003
00000100 04 004
00000101 05 005
00000110 06 006
00000111 07 007
00001000 08 008
00001001 09 009
00001010 0A 010
00001011 0B 011
00001100 0C 012
00001101 0D 013
00001110 0E 014
00001111 0F 015
00010000 10 016
00010001 11 017
00010010 12 018
00010011 13 019
00010100 14 020
00010101 15 021
00010110 16 022
00010111 17 023
00011000 18 024
00011001 19 025
00011010 1A 026
00011011 1B 027
00011100 1C 028
00011101 1D 029
00011110 1E 030
00011111 1F 031
00100000 20 032  
00100001 21 033 !
00100010 22 034 "
00100011 23 035 #
00100100 24 036 $
00100101 25 037 %
00100110 26 038 &
00100111 27 039 '
00101000 28 040 (
00101001 29 041 )
00101010 2A 042 *
00101011 2B 043 +
00101100 2C 044 ,
00101101 2D 045 -
00101110 2E 046 .
00101111 2F 047 /
00110000 30 048 0
00110001 31 049 1
00110010 32 050 2
00110011 33 051 3
00110100 34 052 4
00110101 35 053 5
00110110 36 054 6
00110111 37 055 7
00111000 38 056 8
00111001 39 057 9
00111010 3A 058 :
00111011 3B 059 ;
00111100 3C 060 <
00111101 3D 061 =
00111110 3E 062 >
00111111 3F 063 ?
01000000 40 064 @
01000001 41 065 A
01000010 42 066 B
01000011 43 067 C
01000100 44 068 D
01000101 45 069 E
01000110 46 070 F
01000111 47 071 G
01001000 48 072 H
01001001 49 073 I
01001010 4A 074 J
01001011 4B 075 K
01001100 4C 076 L
01001101 4D 077 M
01001110 4E 078 N
01001111 4F 079 O
01010000 50 080 P
01010001 51 081 Q
01010010 52 082 R
01010011 53 083 S
01010100 54 084 T
01010101 55 085 U
01010110 56 086 V
01010111 57 087 W
01011000 58 088 X
01011001 59 089 Y
01011010 5A 090 Z
01011011 5B 091 [
01011100 5C 092 \
01011101 5D 093 ]
01011110 5E 094 ^
01011111 5F 095 _
01100000 60 096 `
01100001 61 097 a
01100010 62 098 b
01100011 63 099 c
01100100 64 100 d
01100101 65 101 e
01100110 66 102 f
01100111 67 103 g
01101000 68 104 h
01101001 69 105 i
01101010 6A 106 j
01101011 6B 107 k
01101100 6C 108 l
01101101 6D 109 m
01101110 6E 110 n
01101111 6F 111 o
01110000 70 112 p
01110001 71 113 q
01110010 72 114 r
01110011 73 115 s
01110100 74 116 t
01110101 75 117 u
01110110 76 118 v
01110111 77 119 w
01111000 78 120 x
01111001 79 121 y
01111010 7A 122 z
01111011 7B 123 {
01111100 7C 124 |
01111101 7D 125 }
01111110 7E 126 ~
01111111 7F 127
10000000 80 128
10000001 81 129
10000010 82 130
10000011 83 131
10000100 84 132
10000101 85 133
10000110 86 134
10000111 87 135
10001000 88 136
10001001 89 137
10001010 8A 138
10001011 8B 139
10001100 8C 140
10001101 8D 141
10001110 8E 142
10001111 8F 143
10010000 90 144
10010001 91 145
10010010 92 146
10010011 93 147
10010100 94 148
10010101 95 149
10010110 96 150
10010111 97 151
10011000 98 152
10011001 99 153
10011010 9A 154
10011011 9B 155
10011100 9C 156
10011101 9D 157
10011110 9E 158
10011111 9F 159
10100000 A0 160
10100001 A1 161
10100010 A2 162
10100011 A3 163
10100100 A4 164
10100101 A5 165
10100110 A6 166
10100111 A7 167
10101000 A8 168
10101001 A9 169
10101010 AA 170
10101011 AB 171
10101100 AC 172
10101101 AD 173
10101110 AE 174
10101111 AF 175
10110000 B0 176
10110001 B1 177
10110010 B2 178
10110011 B3 179
10110100 B4 180
10110101 B5 181
10110110 B6 182
10110111 B7 183
10111000 B8 184
10111001 B9 185
10111010 BA 186
10111011 BB 187
10111100 BC 188
10111101 BD 189
10111110 BE 190
10111111 BF 191
11000000 C0 192
11000001 C1 193
11000010 C2 194
11000011 C3 195
11000100 C4 196
11000101 C5 197
11000110 C6 198
11000111 C7 199
11001000 C8 200
11001001 C9 201
11001010 CA 202
11001011 CB 203
11001100 CC 204
11001101 CD 205
11001110 CE 206
11001111 CF 207
11010000 D0 208
11010001 D1 209
11010010 D2 210
11010011 D3 211
11010100 D4 212
11010101 D5 213
11010110 D6 214
11010111 D7 215
11011000 D8 216
11011001 D9 217
11011010 DA 218
11011011 DB 219
11011100 DC 220
11011101 DD 221
11011110 DE 222
11011111 DF 223
11100000 E0 224
11100001 E1 225
11100010 E2 226
11100011 E3 227
11100100 E4 228
11100101 E5 229
11100110 E6 230
11100111 E7 231
11101000 E8 232
11101001 E9 233
11101010 EA 234
11101011 EB 235
11101100 EC 236
11101101 ED 237
11101110 EE 238
11101111 EF 239
11110000 F0 240
11110001 F1 241
11110010 F2 242
11110011 F3 243
11110100 F4 244
11110101 F5 245
11110110 F6 246
11110111 F7 247
11111000 F8 248
11111001 F9 249
11111010 FA 250
11111011 FB 251
11111100 FC 252
11111101 FD 253
11111110 FE 254
11111111 FF 255

    Finally, here is the source to the library itself which was included by main.c at the top of the post.

    chastelib.h

    /*
This file is a library of functions written by Chastity White Rose. The functions are for converting strings into integers and integers into strings. I did it partly for future programming plans and also because it helped me learn a lot in the process about how pointers work as well as which features the standard library provides and which things I need to write my own functions for.
*/

/* These two lines define a static array with a size big enough to store the digits of an integer including padding it with extra zeroes. The function which follows always returns a pointer to this global string and this allows other standard library functions such as printf to display the integers to standard output or even possibly to files.*/

#define usl 32
char int_string[usl+1]; /*global string which will be used to store string of integers*/

 /*radix or base for integer output. 2=binary, 8=octal, 10=decimal, 16=hexadecimal*/
int radix=2;
/*default minimum digits for printing integers*/
int int_width=1;

/*
This function is one that I wrote because the standard library can display integers as decimai, octai, or hexadecimal but not any other bases(including binary which is my favorite). My function corrects this and in my opinion such a function should have been part of the standard library but I'm not complaining because now I have my own which I can use forever!
*/

char* intstr(unsigned int i)
{
 int width=0;
 char *s=int_string+usl;
 *s=0;
 while(i!=0 || width<int_width)
 {
  s--;
  *s=i%radix;
  i/=radix;
  if(*s<10){*s+='0';}else{*s=*s+'A'-10;}
  width++;
 }

 return s;
}

/*
This function is my own replacement for the strtol function from the C standard library. I didn't technically need to make this function because the functions from stdlib.h can already convert strings from bases 2 to 36 into integers. However my function is simpler because it only requires 2 arguments instead of three and it also does not handle negative numbers. Never have I needed negative integers but if I ever do I can use the standard functions or write my own in the future.
*/

int strint(char *s)
{
 int i=0;
 char c;
 if( radix<2 || radix>36 ){printf("Error: radix %i is out of range!\n",radix);return i;}
 while( *s == ' ' || *s == '\n' || *s == '\t' ){s++;} /*skip whitespace at beginning*/
 while(*s!=0)
 {
  c=*s;
  if( c >= '0' && c <= '9' ){c-='0';}
  else if( c >= 'A' && c <= 'Z' ){c-='A';c+=10;}
  else if( c >= 'a' && c <= 'z' ){c-='a';c+=10;}
  else if( c == ' ' || c == '\n' || c == '\t' ){return i;}
  else{printf("Error: %c is not an alphanumeric character!\n",c);return i;}
  if(c>=radix){printf("Error: %c is not a valid character for radix %i\n",*s,radix);return i;}
  i*=radix;
  i+=c;
  s++;
 }
 return i;
}

/*
this function prints a string using fwrite
This is the best C representation of how my Assembly programs also work/
*/

void putstring(char *s)
{
 int c=0;
 char *p=s;
 while(*p++){c++;} 
 fwrite(s,1,c,stdout);
}

void putint(unsigned int i)
{
 putstring(intstr(i));
}

  • Chastity’s Source for ELF 32-bit executable creation

    I wrote an example program using a custom made ELF-32 header using data declaration statements. I wrote many comments which reference the official specification. This was an exercise both in programming and also Technical Reading and Writing. I had to read enough of the specification PDF file to understand what I was doing. I then tried to write descriptive comments that at the very least I would understand when I need to remind myself how this format is created.

    ;Chastity's Source for ELF 32-bit executable creation
;
;All data as defined in this file is based off of the specification of the ELF file format.
;I first looked at the type of file created by FASM's "format ELF executable" directive.
;It is great that FASM can create an executable file automatically. (Thanks Tomasz Grysztar, you are a true warrior!)
;However, I wanted to understand the format for theoretical use in other assemblers like NASM.

;The Github repository with the spec I used is here.
;<https://github.com/xinuos/gabi>
;And this is the wikipedia article which linked me to the specification document
;<https://en.wikipedia.org/wiki/Executable_and_Linkable_Format>

;This file contains a raw binary ELF32 header created using db,dw,dd commands.
;After that, it proceeds to assemble a real "Hello World!" program

;Header for 32 bit ELF executable (with comments based on specification)

db 0x7F,"ELF" ;ELFMAGIC: 4 bytes that identify this as an ELF file. The magic numbers you could say.
db 1          ;EI_CLASS: 1=32-bit 2=64-bit
db 1          ;EI_DATA: The endianness of the data. 1=ELFDATA2LSB 2=ELFDATA2MSB For Intel x86 this is always 1 as far as I know.
db 1          ;EI_VERSION: 1=EV_CURRENT (ELF identity version 1) (which is current at time of specification Version 4.2 I was using)
db 9 dup 0    ;padding zeros to bring us to address 0x10
dw 2          ;e_type: 2=ET_EXEC (executable instead of object file)
dw 3          ;e_machine : 3=EM_386 (Intel 80386)
dd 1          ;e_version: 1=EV_CURRENT (ELF object file version.)

p_vaddr=0x8048000
e_entry=0x8048054 ;we will be reusing this constant later 

dd e_entry    ;e_entry: the virtual address at which the program starts
dd 0x34       ;e_phoff: where in the file the program header offset is
db 8 dup 0    ;e_shoff and e_flags are unused in this example,therefore all zeros
dw 0x34       ;e_ehsize: size of the ELF header
dw 0x20       ;e_phentsize: size of program header which happens after ELF header
dw 1          ;e_phnum: How many program headers. Only 1 in this case
dw 0x28       ;e_shentsize: Size of a section header
dw 0          ;e_shnum number of section headers
dw 0          ;e_shstrndx: section header string index (not used here)

;That is the end of the 0x34 byte (52 bytes decimal) ELF header. Sadly, this is not the end and a program header is also required (what drunk person made this format?)

dd 1          ;p_type: 1=PT_LOAD
dd 0          ;p_offset: Base address from file (zero)
dd p_vaddr    ;p_vaddr: Virtual address in memory where the file will be.
dd p_vaddr    ;p_paddr: Physical address. Same as previous

image_size=0x1000 ;Chosen size for file and memory size. At minimum this must be as big as the actual binary file (code after header included)
                  ;By choosing a default size of 0x1000, I am assuming all assembly programs I write will be less than 4 kilobytes

dd image_size  ;p_filesz: Size of file image of the segment. Must be equal to the file size or greater
dd image_size  ;p_memsz: Size of memory image of the segment, which may be equal to or greater than file image.

dd 7           ;p_flags: permission flags: 7=4(Read)+2(Write)+1(Execute)
dd 0           ;p_align; Alignment (none)

;important FASM directives
use32          ;tell assembler that 32 bit code is being used
org e_entry    ;origin of new code begins at the entry point

;now, the actual hello world program
mov eax,4      ;invoke SYS_WRITE (kernel opcode 4 on 32 bit systems)
mov ebx,1      ;write to the STDOUT file
mov ecx,msg    ;pointer/address of string to write
mov edx,13     ;number of bytes to write
int 80h

mov eax,1 ;function SYS_EXIT (kernel opcode 1 on 32 bit systems)
mov ebx,0 ;return 0 status on exit - 'No Errors'
int 80h   ;call Linux kernel with interrupt

msg db 'Hello World!',0Ah

;This is the makefile I use when assembling and running this program

;main-fasm:
;	fasm ELF-32-hello.asm
;	chmod +x ELF-32-hello.bin
;	./ELF-32-hello.bin

    I made a repository for examples like this. Others may want to understand the header used on Linux systems.

    https://github.com/chastitywhiterose/ELF

  • The Bitwise Operations

    There are 5 bitwise operations which operate on the bits of data in a computer. For the purpose of demonstration, it doesn’t matter which number the bits represent at the moment. This is because the bits don’t have to represent numbers at all but can represent anything described in two states. Bits are commonly used to represent statements that are true or false. For the purposes of this section, the words AND, OR, XOR are in capital letters because their meaning is only loosely related to the Englist words they get their name from.

    Bitwise AND Operation

    0 AND 0 == 0
0 AND 1 == 0	
1 AND 0 == 0
1 AND 1 == 1

    Think of the bitwise AND operation as multiplication of single bits. 1 times 1 is always 1 but 0 times anything is always 0. That’s how I personally think of it. I guess you could say that something is true only if two conditions are true. For example, if I go to Walmart AND do my job then it is true that I get paid.

    Bitwise OR Operation

    0 OR 0 == 0
0 OR 1 == 1	
1 OR 0 == 1
1 OR 1 == 1

    The bitwise OR operation can be thought of as something that is true if one or two conditions are true. For example, it is true that playing in the street will result in you dying because you got run over by a car. It is also true that if you live long enough, something else will kill you. Therefore, the bit of your impending death is always 1.

    Bitwise XOR Operation

    0 XOR 0 == 0
0 XOR 1 == 1	
1 XOR 0 == 1
1 XOR 1 == 0

    The bitwise XOR operation is different because it isn’t really used much for evaluating true or false. Instead, it is commonly used to invert a bit. For example, if you go back to the source of my graphics programs in Chapter 2, you will see that most of those programs contain the statement:

    index^=1;

    If you look at my XOR chart above, you will see that using XOR of any bit with a 1 causes the result to be the opposite of the original bit. In the context of those programs, the index variable is meant to be 0 to represent black and 1 to represent white. The XOR operation is the quickest way to achieve this bit inversion. In fact, in all my years of programming, that’s pretty much the only thing I have used it for!

    Bitwise Left and Right Shift Operations

    Consider the case of the following 8 bit value:

    00001000

    This would of course represent the number 8 because a 1 is in the 8’s place value. We can left shift or right shift.

    00001000 ==  8 : is the original byte

00010000 == 16 : after left shift
00000100 ==  4 : after right shift

    Left and right shift operations allow us to multiply or divide a number by 2 by taking advantage of the base 2 system. These shifts are essential in graphics programming because sometimes to need to extract the red, green, or blue values separately out of their 24 bit representation. For example, consider this code:

       pixel=p[x+y*width];
   r=(pixel&0xFF0000)>>16;
   g=(pixel&0x00FF00)>>8;
   b=(pixel&0x0000FF);

    The first statement gets the pixel out of an array of data which is indexed by x and y geometric coordinates. This will be a 24 bit value, or in some cases 32 bit with the highest 8 bits representing the alpha or transparency level.

    variables r,g,b represent red, green, and blue. With clever use of bitwise AND operations and right shifting by the correct number of bits, it is possible to extract just that color component to be modified. Without the ability to do this, my graphics animations and my Tetris game would never have been possible. The colors had to be exactly sent to the drawing functions. This is true not just for SDL but using any graphical system involving colors.

    Learning More

    I know I covered a lot in this chapter but I encourage you to learn about the binary numeral system and its close cousin the hexadecimal system. If you do an online search, you will find courses, tutorials, and videos by millions of people who can probably explain these same concepts in a way that you understand better if you are still confused after reading this chapter!