source: buchla-68k/lib700/mangle.c

/*
   =============================================================================
        mangle.c -- mangle a bit stream
        Version 2 -- 1987-08-28 -- D.N. Lynx Crowe
        (c) Copyright 1987 - D.N. Lynx Crowe
   =============================================================================
*/

/*
   =============================================================================
        mangle(bitmap, nb, ib) -- reorder the 'nb' least significant bits
        in 'ib' according to 'bitmap'.  Assumes that 'bitmap' is at least 'nb'
        words long, and that nb <= 32.  The 'bitmap' translation table contains
        an output word for each bit in the input word, with each 'bitmap' entry
        corresponding to the bit number matching its index.  For example,
        'bitmap[0]' contains the word which will be 'OR'ed into the output if
        the least significant bit of the input word is set, while 'bitmap[31]'
        corresponds to the most significant bit of the input word.
   =============================================================================
*/

#include "ram.h"

int32_t mangle(int32_t *bitmap, int16_t nb, int32_t ib)
{
        register int32_t        bm;                     /* scan mask */
        register int32_t        rv;                     /* result value */
        register int16_t        bn;                     /* bit number (bitmap index) */

        bm = 0x00000001L;                       /* setup scan mask */
        rv = 0x00000000L;                       /* clear the output word */

        for (bn = 0; bn < nb; bn++) {           /* scan across nb bits */

                if (ib & bm)                    /* if the input bit is 1 */
                        rv |= bitmap[bn];       /* 'OR' the bitmap into rv */

                bm <<= 1;                       /* shift the scan mask left */
        }

        return(rv);                             /* return rv as the result */
}