[Icc-avr] Const arrays of pointers to const arrays

[Björn Lindgren]

Sorry, it didn't work in assembler. It seemed like it did with the condensed
data of 6 bytes below, but with full data range ( 2kbyte) it doesn't.
Basically I want to get rid of:
	if( 0 == key ) {
		start_a = ptr_a = &sinus_tab[7][0]; // 0
		start_b = ptr_b = &sinus_tab[3][0];
	}
	else if( 1 == key ) {
		start_a = ptr_a = &sinus_tab[4][0]; // 1
		start_b = ptr_b = &sinus_tab[0][0];
	}
...etc...
	else if( 15 == key ) {
		start_a = ptr_a = &sinus_tab[5][0]; // 2
		start_b = ptr_b = &sinus_tab[0][0];
	}
and replace it by a look-up table.

Björn



>From: "Björn Lindgren" <bjonaspero at hotmail.com>
>Date: Wed, 05 Sep 2007 09:46:19 +0200
>
>Can someone tell me how to define a constant array of pointers to other 
>constant arrays.
>I can do this in assembler but I want the customer to take over the 
>maintenance and therefore
>I wish to have 100% of the code in C.
>
>Here’s a condensed version:
>
>// pointer_test.c
>
>const signed char sinus_tab[2][3] = {
>{1,2,3},{4,5,6}};
>
>/*** Viritual definition (I want something like this)
>const signed char *pointer[2]  = {
>	sinus_tab[1],
>	&sinus_tab[0][0]  };*/
>
>// Working declaration (while the definition is done in assembler)
>extern const unsigned int pointer[2];
>
>// Usage:
>const signed char *get_pointer( unsigned char index )  {
>
>	return (void *)pointer[ index ];
>}
>In assenmler (i.e. wanted result):
>	.area lit(rom, con, rel)
>_pointer::
>	.word _sinus_tab+3
>	.word _sinus_tab
>
>The first constant array (sinus_tab) is ok but the second either
>ends up in ‘idata’ (initiated SRAM) or, I get error message like:
>
>cast from `pointer to const signed char' to `unsigned int' is illegal in 
>constant expressions
>
>Thanx for help
>Björn Lindgren
>
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