Deagels lab1 submission

ANSWERS.md

@@ -19,128 +19,244 @@ Please use [markdown](https://help.github.com/articles/markdown-basics) formatin
 
 Make another directory inside the `unixstuff` directory called `backups`
 
-**Answer:** *YOUR ANSWER HERE*
+**Answer:** `~/unixstuff$ mkdir backups`
 
 ###Exercise 1b
 
 Use the commands `cd`, `ls` and `pwd` to explore the file system.
 
 (Remember, if you get lost, type `cd` by itself to return to your home-directory)
 
-**Answer:** *YOUR ANSWER HERE*
+**Answer:** `cd backups` `pwd` `cd ..` `ls`
 
 ###Exercise 2a
 
 Create a backup of your `science.txt` file by copying it to a file called `science.bak`
 
-**Answer:** *YOUR ANSWER HERE*
+**Answer:** `cp -T sci[tab] science.bak`
 
 ###Exercise 2b
 
 Create a directory called `tempstuff` using `mkdir`, then remove it using the `rmdir` command.
 
-**Answer:** *YOUR ANSWER HERE*
+**Answer:** `mkdir tempstuff` `rmdir tem[tab]`
 
 ###Exercise 3a
 
 Using the above method, create another file called `list2` containing the following fruit: orange, plum, mango, grapefruit. Read the contents of `list2`.
 
-**Answer:** *YOUR ANSWER HERE*
-
+**Answer:**
+```
+cat > list2
+orange
+plum
+mango
+grapefruit
+^D
+cat list2
+```
 ###Exercise 3b
 
 Using pipes, display all lines of `list1` and `list2` containing the letter 'p', and sort the result.
 
-**Answer:** *YOUR ANSWER HERE*
+**Answer:** `grep p list1 list2 | sort` 
 
 ###Exercise 5a
 
 Try changing access permissions on the file `science.txt` and on the directory `backups`.
 
 Use `ls -l` to check that the permissions have changed.
 
-**Answer:** *YOUR ANSWER HERE*
+**Answer:** `chmod go+rw science.txt` `chmod go-rwx backups` `ls -l`
 
 ##Shell questions
 
 1. What option with the command `rm` is required to remove a directory?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `-r`, `-R` or  `-recursive`
 1. What is the command used to display the manual pages for any command?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `man <cmd>` or  `help <cmd>`, `whatis <cmd>`, `info <cmd>`
 1. What command will show the first 5 lines of an input file?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `head -n 5 <file>`
 1. What command can be used to rename a file?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `mv <oldfile> <newfile>` or `rename <old> <new> <file(s)>`
 1. What option can we given to `ls` to show the hidden files?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `-a`
 1. What will the command `cat -n file` do?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** Prints contents of file with enumerated lines.
 1. What will the command `echo -n hello` do?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** Prints "hello" without automatically appending a newline char.
 1. What command will display s list of the users who currently logged in in the system?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `who` or `users` (`users | sed 's/ /\n/g' | uniq`)
 1. How do you change password on your account?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `passwd`
 1. How can you list a file in reverse order?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `tac <file>` (linewise)
 1. What does the `less` command do?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** Lazily reads files and allows for backtracing. 
 1. With `less` how do you navigate?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** [space] for next page
 1. What command will display the running processes of the current user?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `ps` `pstree` `top` `top??`
 1. What command can be used to find the process(es) consuming the most CPU?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `top`
 
 ##vi questions
 1. How do we save a file in `vi` and continue working?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `:w[Enter]` in normal-mode
 1. What command/key is used to start entering text?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `i`
 1. What are the different modes the editor can be in?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** normal / insert / visual / select / command-line / ex-mode
 1. What command can be used to place the cursor at the beginning of line 4?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `4gg`, `4G` or `:4[Enter]`
 1. What will `dd` command do (in command-mode)?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** dd is a linewise delete function
 1. How do you undo the most recent changes?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `u` `:undo[Enter]`
 1. How do you move back one word?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `b`
 
 ##The C Language and Make tool Questions
 
 1. How do you use `gcc` to only produce the `.o` file?  What is the difference between generating only the `.o` file, and building the `hello` executable done in the previous compilation above?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `gcc -c <sourcefile>` The object file is not linked
 1. Give the command for compiling with `debug` enabled instead of normal compilation for the two examples shown in Listing 2 and Listing 3. Explain how to turn debugging on/off for the two cases.
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** Listing 2: `gcc -DDEBUG <sourcefile>`, `-g` is similar but does not define anything. *(NDEBUG may however NOT be defined) 
+  Listing 3: global var `debug` must be changed in source in order to toggle.
 1. Give a brief pros and cons discussion for the two methods to add debug code shown in Listing 2 and Listing 3.
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** Listing 2 requires compile time config but is efficient. Listing 3 can potentially be toggled during runtime but may cause efficiency reduction in tight loops regardless of mode (if self modification is not allowed/implemented)
 1. Provide the command for generating the *map* file. Which of the `gcc` tools is responsible for producing a *map* file?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `-Wl,-Map=mymap.map` (`-Wl,-Map,mymap.map` for non-GNU). Arguments are passed on as linker is not part of gcc
 1. What is the content of each of the sections in a *map* file. Explain briefly.
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** The map shows address resolutions, .data, .code, etc sections size and position, archive members included and allocated symbols and their assigned value.
 1. Rewrite `hello.c` to produce entries in the *map* file for `.data`, `.bss`, and `.rodata`. Hint: This can be done by adding one variable for each type to the file.
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:**
+```
+const char debug_cmt[] = "Some smart debugcomment\n";
+const char hello[]     = "Hello world!\n";
+const int  retval      = 0;
+```
 1. Add the following function to `hello.c`: `double multiply(double x1, double x2)`, which returns `x1*x2`. Use `gcc` to generate an assembly code listing for the program, and examine the assembly code. What assembly instructions are used to do this? Repeat this task, but now replace `double` with `float`. Explain!
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `gcc -O -S dmult.c` (took the liberty of optimizing)
+  Examining dmult.s & fmult.s: `mulsd    %xmm1, %xmm0` scalar double as opposed to `mulss    %xmm1, %xmm0` scalar single mult. instruction. Single (float) operates on half the bit-size of double. It is thus curious how gcc chooses to use the 128bit XMM registers on both accounts.
 1. How does `make` know if a file must be recompiled?
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** The source file is 'newer' than the currently compiled file, or the file does not exist.
 1. Provide a `make` command to use a file named `mymakefile` instead of the default `makefile`.
-  - **Answer:** *YOUR ANSWER HERE*
+  - **Answer:** `make -f mymakefile`
 1. How do you implement an *include guard*, and why is it needed?
-  - **Answer:** *YOUR ANSWER HERE*
-
+  - **Answer:** Include guards prevent common libraries and headers being imported several times. It looks like this:
+```
+#ifndef IVEBEENHEREBEFORE
+#define IVEBEENHEREBEFORE
+// do header stuff
+#endif
+```
 ##Library Task
 
 Insert your code between the brackets `{}`:
 
-    void main( int argc, char *argv[] )
-	{
+**main.c:**
+```
+#include <stdio.h>
+#include <stdint.h>
+#include <time.h>
+#include <stdlib.h>
+// TODO: #include "l1.c"
+
+int main( int argc, char *argv[] )
+{
+    uint8_t debug = 0;
+    int size = 8;
+    double min = 0.0;
+    double range = 100.0;
+    int i;
+    char *p;
+    for ( i = 1; i < argc; i++ )
+    {
+        if ( !strcmp( argv[i], "-r" )) // range
+        {
+            range = strtod( argv[++i], &p );
+	    if ( !range )
+            {
+                printf( "Argument to -r must be a positive number.\n" );
+		exit(1);
+            }
+        }
+	else if ( !strcmp( argv[i], "-m" )) // minimum
+        {
+            min = strtod( argv[++i], &p );
+        }
+	else if ( !strcmp( argv[i], "-s" )) // table size
+        {
+            size = strtod( argv[++i], &p );
+        }
+	else if ( !strcmp( argv[i], "-d" )) // debug
+        {
+            debug = -1;
+            for ( i = 1; i < argc; i++ )
+            {
+                printf( "argv[%i]: \"%s\"\n", i, argv[i] );
+            }
+        }
+    }
+    double div = RAND_MAX / range;
+    double table[size];
+
+    if ( debug )
+    {
+        printf( "table size: %i\nminimum:    %.2f\nrange:      %.2f", size, min, range );
     }
-
-	double tab_sort_sum( double *tab, int tab_size )
-	{
-	}
 
+    srand( time( NULL )); // seed random generator
+    for ( i = size; i >= 0; i-- )
+    {
+        table[i] = min + ((double) rand()) / div;
+    }
+
+    double sum = 0.0; //TODO: tab_sort_sum( &table, size );
+
+    /*
+    int cell_width = 4; // TODO: log_2( max ) + 3
+    char *formatstr[6];
+    sprintf( formatstr, '%%%dd\n', cell_width ); // e.g. '%10d'
+    const char *format[] = (const char *) formatstr;
+    */
+    const char format[] = "%8.2f\n";
 
+    for ( i = 0; i < size; i++ ) // each row
+    {
+        printf( format, table[i] );
+    }
+    printf( "SUM: %f\n", sum );
+    return 0;
+}
+```
+**l1.c:**
+unfinished
+```
+#include <stdlib.h>
+
+int *cmp( const double *a, const double *b )
+{
+    if ( *a > *b ) return 1;
+    if ( *a < *b ) return -1;
+    return 0;
+}
+
+double tab_sort_sum( double *tab, int tab_size )
+{
+    qsort( tab, tab_size, sizeof(*tab), cmp );
+    double sum = 0;
+    int i;
+    for ( i = 0; i >= 0; i-- )
+    {
+        sum += tab[i];
+    }
+    return sum;
+}
+```
+**makefile:**
+```
+main: main.c l1.c
+    gcc main.c -O -o main
+```

dmult.c

@@ -0,0 +1,3 @@
+double multiply( double x, double y ) {
+	return x * y;
+}

dmult.s

@@ -0,0 +1,14 @@
+	.file	"dmult.c"
+	.text
+.globl multiply
+	.type	multiply, @function
+multiply:
+.LFB0:
+	.cfi_startproc
+	mulsd	%xmm1, %xmm0
+	ret
+	.cfi_endproc
+.LFE0:
+	.size	multiply, .-multiply
+	.ident	"GCC: (GNU) 4.4.7 20120313 (Red Hat 4.4.7-4)"
+	.section	.note.GNU-stack,"",@progbits

fmult.c

@@ -0,0 +1,3 @@
+float multiply( float x, float y ) {
+	return x * y;
+}

fmult.s

@@ -0,0 +1,14 @@
+	.file	"fmult.c"
+	.text
+.globl multiply
+	.type	multiply, @function
+multiply:
+.LFB0:
+	.cfi_startproc
+	mulss	%xmm1, %xmm0
+	ret
+	.cfi_endproc
+.LFE0:
+	.size	multiply, .-multiply
+	.ident	"GCC: (GNU) 4.4.7 20120313 (Red Hat 4.4.7-4)"
+	.section	.note.GNU-stack,"",@progbits

l1.c

@@ -0,0 +1,21 @@
+#include <stdlib.h>
+
+int *cmp( const double *a, const double *b )
+{
+    if ( *a > *b ) return 1;
+    if ( *a < *b ) return -1;
+    return 0;
+}
+
+double tab_sort_sum( double *tab, int tab_size )
+{
+    qsort( tab, tab_size, sizeof(*tab), cmp );
+    double sum = 0;
+    int i;
+    for ( i = 0; i >= 0; i-- )
+    {
+        sum += tab[i];
+    }
+    return sum;
+}
+