c - assignment of packed bitfield struct gives wrong values -


i have packed structure should 16 bits:

#pragma pack(1)  typedef unsigned int uint; typedef unsigned short ushort;  typedef struct color color; struct color {     uint r : 5;     uint g : 5;     uint b : 5;     uint _ : 1; };

i have confirmed that

&(((color*)0x06000000)[x]) == &(((ushort*)0x06000000)[x])

for various values of x. however, in code, these 2 lines give me different results.

void write_pixel (uint x, uint y, color color) {     #if 0     ((color*)0x06000000)[x+y*240] = color;     #else      ((ushort*)0x06000000)[x+y*240] = ((ushort*)&color)[0];     #endif }

with second option being correct.

what cause?

note. i'm compiling gba emulator no debugger or printf, yes/no statements way of green/red pixel.

the problem value seen parameter list going (due promotion of parameters) unsigned int (32bits). incorrect line trying copy 32bit unsigned int 16bit short.

normally work pragma modifies how 16bit color being placed in promoted parameter and/or how code referencing 16bits of color.

while packed values (normally) not promoted, if there no prototype called function parameters assumed 'int'  code assumes data (sizeof int) bytes long (4 bytes) , assignment takes last 2 bytes of 4 byte value rather first 2 bytes.

Comments

Post a Comment

Popular posts from this blog

cakephp - simple blog with croogo -

i not problem, made simple blog in croogo, problem is not adding or modifying or delete, because arabic language ?? function add in controller `public function admin_add() { $this->set('title_for_layout', __('add part')); if (!empty($this->request->data)) { $this->part->create(); if ($this->part->save($this->request->data)) { $this->session->setflash(__('the part has been saved'), 'default', array('class' => 'success')); $this->redirect(array('action' => 'index'));//, $this->part->id)); } else { $this->session->setflash(__('the part not saved. please, try again.'), 'default', array('class' => 'error')); } } }` => model `class part extends appmodel { public $name = 'part'; var $belongst...
Read more

How to group boxplot outliers in gnuplot -

i have large set of data points. try plot them boxplot, of outliers exact same value , represented on line beside each other. found how set horizontal distance between outliers in gnuplot boxplot , doesn't much, apparently not possible. is possible group outliers together, print 1 point , print number in brackets beside indicate how many points there are? think make more readable in graph. for information, have 3 boxplots 1 x value , times 6 in 1 graph. using gnuplot 5 , played around pointsize, doesn't reduce distance anymore. hope can help! edit: set terminal pdf set output 'dat.pdf' file0 = 'dat1.dat' file1 = 'dat2.dat' file2 = 'dat3.dat' set pointsize 0.2 set notitle set xlabel 'x' set ylabel 'y' header = system('head -1 '.file0); n = words(header) set xtics ('' 1) set [i=1:n] xtics add (word(header, i) i) set style data boxplot plot file0 using (1-0.25):1:(0.2) boxplot lw 2 lc rgb '#8b0000...
Read more

bash - Performing variable substitution in a string -

i have string contains use of variable, , i'd substitute variable's value string. right best have is #!/bin/bash foo='$name; echo bar' name="the name" expanded="$(eval echo "$foo")" echo "$expanded" which has obvious defects: prints the name bar while i'd print the name; echo bar instead of eval can bash's regex matching bash's string replacement: foo='$name; echo bar' name="the name" [[ "$foo" =~ \$([[:alnum:]]+) ]] && s="${!bash_rematch[1]}" && expanded="${foo/\$${bash_rematch[1]}/$s}" echo "$expanded" name; echo bar
Read more