Thread: Help with macro

I need to implement a macro for a byte x , which is represented by

0 1 2 3 4 5 6 7
blink bg red bg green bg blue intensity fg red fg green fg blue

Each of the bits is having this attribute . I need to implement 3 macros.

Code:

#ifndef TEXTMODE_H
#define TEXTMODE_H


#define T_BLINK 0x80
#define T_INTENSITY 0x08
#define T_RED 0x04
#define T_GREEN 0x02
#define T_BLUE 0x01

/* DESCRIPTION:
 * ------------
 * Modifies the attribute byte x by setting the attribute attr. If the attribute
 * is already set, the attribute byte remains unchanged.
 *
 * The attribute bytes are defined in the beginning of this header file.
 *
 * ARGUMENTS:
 * ------------
 * x: the attribute byte.
 * attr: the attribute bit to set as active (1).
 *
 */
#define SETATTR(x, attr) ((x) |= (attr))





/* DESCRIPTION:
 * ------------
 * Modifies the attribute byte x by setting the foreground and background color.
 *
 * This has no effect on the blink and intensity bits or the color bits already
 * set. For example, if the color is already red and SETCOLOR is used to set the
 * color to be green, then the attribute byte has both red and green set.
 *
 * See above for the definitions for different colors (T_RED, T_GREEN, T_BLUE).
 * The same definitions are used for both foreground and background colors.
 *
 * ARGUMENTS:
 * ------------
 * x: the attribute byte.
 * bg: the background color.
 * fg: the foreground color.
 *
 */
#define SETCOLOR(x, bg, fg)((x) |= (bg | fg))




/* DESCRIPTION:
 * ------------
 * Modifies the attribute byte by setting the color bits to 0 (black color).
 * This has no effect on the blink and intensity bits.
 *
 * ARGUMENTS:
 * ------------
 * x: the attribute byte.
 *
 */
#define RESETCOLOR(x)((x) &= ~(T_GREEN | T_BLUE| T_RED))


#endif

My SETCOLOR macro implementation is giving wrong results. Please give a correct implementation. Also please see that others are implemented properly or not.

can you give an example of (exactly) how you use SETCOLOR when it doesn't work properly?

Originally Posted by dmh2000

can you give an example of (exactly) how you use SETCOLOR when it doesn't work properly?

attr = 0x00


SETATTR(attr, T_BLINK); // attr is blinking, black on black (0x80)
SETCOLOR(attr, T_RED, T_GREEN); // attr is blinking, green on red (0xC2).
SETCOLOR(attr, T_BLUE, T_RED); // attr is blinking, red+green on blue+red (0xD6).
RESETCOLOR(attr); // attr is blinking, black on black (0x80)
SETCOLOR(attr, 0, T_GREEN); // attr is blinking, green on black (0x82)
SETATTR(attr, T_INTENSITY); // attr is blinking and has high intensity, green on black (0x8A).

Originally Posted by spanlength

attr = 0x00


SETATTR(attr, T_BLINK); // attr is blinking, black on black (0x80)
SETCOLOR(attr, T_RED, T_GREEN); // attr is blinking, green on red (0xC2).
SETCOLOR(attr, T_BLUE, T_RED); // attr is blinking, red+green on blue+red (0xD6).
RESETCOLOR(attr); // attr is blinking, black on black (0x80)
SETCOLOR(attr, 0, T_GREEN); // attr is blinking, green on black (0x82)
SETATTR(attr, T_INTENSITY); // attr is blinking and has high intensity, green on black (0x8A).

For SETCOLOR i did the following
#define SETCOLOR(x, bg, fg)((x) |= ((bg << 4) | (fg)))

and for RESETCOLOR
#define RESETCOLOR(x)((x) &= 0x88)

Let me know if correct or not.

Consider the following:

Code:

#define T_BLINK      0x80
#define T_INTENSITY  0x08

#define T_RED        0x44
#define T_GREEN      0x22
#define T_BLUE       0x11

#define T_ATTR_MASK  0x88
#define T_COLOR_MASK 0x77
#define T_FG_MASK    0x07
#define T_BG_MASK    0x70

The key point is that the generic color constant has the correct value to set both foreground and background at the same time. Given any color value,

Code:

foreground = (color & T_FG_MASK)
background = (color & T_BG_MASK)
foreandback = (color & T_COLOR_MASK) == (color & (T_FG_MASK | T_BG_MASK))
attribute = (color & T_ATTR_MASK)

To write the macros, first figure out which bits are kept from the old value; doing a bitwise AND with the correct mask keeps those bits and clears the rest.

For the new values, you'll simply need a bitwise OR. Remember to use parentheses around each expression, because the bitwise operator precedence is dicey; better not assume. You'll want to first mask (AND) the correct parts from the macro variable, then OR it to the result. This is the technique I use to work with bit masks; it is universal, not limited to this particular task here.

You should be able to write the macros using the above. I'd like to see your efforts; I'm very willing to help you understand, but I am not going to write the macros for you.