Project Extra Credit: Character Counting
Due: 7 May 
4 May
Requirements Specification
Create the source file jdoe1pec.asm, assembly it, link it, and run
it. When it runs correctly, submit using Blackboard.
(Remember that the jdoe1 is suppose to be your id that you use to
log onto the GL computers, so that there is a unique file!
Do not use jdoe1 unless that is in YOUR ID!!)
Description
For this project you will be working with a text file of unknown
size.
You are to read the file into a buffer, count how many of each
character there is, and print out the counts for the letters of
the alphabet. You are to convert all lowercase letters to
uppercase before counting them. You get the name of the
file from the user.
Set up a buffer of 8192 bytes (8K) since this is more efficient
for the operating system. When you do the reads from the file,
you will get back the number of bytes actually read. If it is
not 8192, you have reached the end of the file.
Hint: Set up an array of 128 integers and use the ASCII code as
an index into the array. (If you wish, you can have an array of
256, if you feel that is a better value.) Make sure your program
will work for counts that are over 1000!
Since you will have counts that go over 256, you can not store
the count in an array of bytes. You will need an array of words
or double words. To get to the correct address of the count to
increment, you need the effective address:
eff = base + offset
The offset is calculated as index times the size of the element
in the array. Assuming you declared an array named counts:
int counts[ 256 ];
Lets assume the base address of the array is 10000.
The effective address of counts[ 0 ] is 10000 + 0 * 4 or 10000
The effective address of counts[ 1 ] is 10000 + 1 * 4 or 10004
The effective address of counts[ 2 ] is 10000 + 2 * 4 or 10008
The effective address of counts[ 3 ] is 10000 + 3 * 4 or 10012
If ebx holds the effective address, then you can use the instruction to increment the count of that character:
inc [ ebx ]
You can use printf, scanf, and any other function in the C library
for this project.
Question: Will the counts be the same for text files that contain a
language other than English? Why?
Filename Input
Scanf Version
push dword prompt
call printf
add esp, 4
push dword fname
push dword spec
call scanf
add esp, 8
(gdb) x/10bc &fname
0x80495ec : 97 'a' 98 'b' 99 'c' 100 'd' 101 'e' 102 'f' 0 '\0' 0 '\0'
0x80495f4 : 0 '\0' 0 '\0'
System Call Version
mov EAX, READ
mov EBX, STDIN
mov ECX, fname
mov EDX, 25
int 80H
mov ebx, eax ; get rid of nl character
dec ebx
mov byte [ fname + ebx ], 0
(gdb) x/10bc &fname
0x80495d4 : 97 'a' 98 'b' 99 'c' 100 'd' 101 'e' 102 'f' 10 '\n'0 '\0'
0x80495dc : 0 '\0' 0 '\0'
Sample output
The output will list the letters and digits and their counts
(User input is in red):
Enter filename: foo.txt
A 413
B 398
C 381
D 379
.
.
.
7 123
8 14
9 1789
System Calls Of Interest
;; The conventions used in Linux 2.2, the parameters are stored in left to right
;; order in the registers EBX, ECX, EDX, EDI, and ESI respectively.
;; The man pages show:
;; int creat(const char *pathname, mode_t mode);
;; mov eax, dword CREATE ; System Call -- open
;; mov ebx, myFile1 ; Pointer to filename
;; mov ecx, O_WRONLY ; Flag for Write Only
;; mov edx, 01FDh ; Mode -- 755 in octal
;; int 80h
;; mov dword [ fdWrite ], eax; save the file descriptor
;; int open(const char *pathname, int flags, mode_t mode);
;; mov eax, dword OPEN ; System Call -- open
;; mov ebx, myFile ; Pointer to filename
;; mov ecx, O_RDONLY ; Flag for Read Only
;; mov edx, 0 ; Mode -- not used to open existing file
;; int 80h
;; mov dword [ fdRead ], eax ; save the file descriptor
;; ssize_t read(int fd, void *buf, size_t count);
;; mov eax, READ ; System Call -- read
;; mov ebx, dword [ fdRead ]; File descriptor opened for reading
;; mov ecx, dword inBuff ; Pointer to input buffer
;; mov edx, dword BUFSIZE ; Number of bytes to read
;; int 80h
;; mov dword [ bytesRead ], eax ; Actual amount read
;; ssize_t write(int fd, const void *buf, size_t count);
;; mov eax, WRITE ; System Call -- write
;; mov ebx, dword [ fdWrite ]; File descriptor opened for writing
;; mov ecx, dword outBuff ; Pointer to output buffer
;; mov edx, dword [ bytesWritten ] ; Number of bytes to write
;; mov 80h
;; int close(int fd);
;; mov eax, CLOSE
;; mov ebx, dword [ fdRead ]
;; int 80h
;;
;; What is this size_t/ssize_t/mode_t stuff?????
;; /usr/src/linux/include/asm-i386/posix_types.h:typedef unsigned short __kernel_mode_t;
;; /usr/src/linux/include/linux/types.h: typedef __kernel_mode_t mode_t;
;; /usr/src/linux/include/asm-i386/posix_types.h:typedef int __kernel_ssize_t;
;; /usr/src/linux/include/linux/types.h: typedef __kernel_ssize_t ssize_t;
;; /usr/src/linux/include/asm-i386/posix_types.h:typedef unsigned int __kernel_size_t
;; /usr/src/linux/include/linux/types.h: typedef __kernel_size_t size_t;
;;
;; in /usr/include/bits/fcntl.h:
;;
;; O_RDONLY 00
;; O_WRONLY 01
;; O_RDWR 02
%define O_RDONLY 00
%define O_WRONLY 01
%define O_RDWR 02
More Defines
Once again, I prefer to give these system call numbers a constant name:
%define READ 3
%define WRITE 4
%define OPEN 5
%define CLOSE 6
%define CREATE 8
OPEN is easier to remember that 5.
Program Header Comment Block
Use the following comment block at the beginning of your source code:
;; Filename: jdoe1p2.asm
;; Name: Ima Student
;; email: jdoe1@umbc.edu
;; Date: 18 Oct 2005
;; Course: CMSC313
;; Description: (Your psuedocode goes here. Must be detailed)
;; Notes: (As needed, such has how to compile)
©2006, Gary L. Burt