/*
=====================================================================
rotate.c
EW  21 Oct 93

A fast 90-degree bit rotation routine.

INPUTS
   src       starting address of 8 x 8 bit source tile
   srcstep   byte offset between adjacent rows in source
   dst       starting address of 8 x 8 bit destination tile
   dststep   byte offset between adjacent rows in destination

RESULTS
   Bits from the source are rotated 90 degrees clockwise and written
   to the destination.

From Sue-Ken Yap, "A Fast 90-Degree Bitmap Rotator," in GRAPHICS GEMS
II, James Arvo ed., Academic Press, 1991, pp. 84-85 and 514-515.

Note that by setting dststep = 1, eight 1-bit rows (1 scanline of an
8-plane bitmap) can be converted to one 8-bit (byte-per-pixel) row,
8 pixels at a time.
===================================================================== */

typedef unsigned long bit32;

#define table( name, n ) \
   static bit32 name[ 16 ] = { \
      0x00000000<<n,0x00000001<<n,0x00000100<<n,0x00000101<<n, \
      0x00010000<<n,0x00010001<<n,0x00010100<<n,0x00010101<<n, \
      0x01000000<<n,0x01000001<<n,0x01000100<<n,0x01000101<<n, \
      0x01010000<<n,0x01010001<<n,0x01010100<<n,0x01010101<<n };

table( ltab0, 0 )
table( ltab1, 1 )
table( ltab2, 2 )
table( ltab3, 3 )
table( ltab4, 4 )
table( ltab5, 5 )
table( ltab6, 6 )
table( ltab7, 7 )


void rotate8x8( unsigned char *src, int srcstep, unsigned char *dst, int dststep )
{
   register unsigned char *p;
   register int    pstep, lonyb, hinyb;
   register bit32  lo, hi;

   lo = hi = 0;

#define extract( d, t ) \
   lonyb = *d & 0xF; hinyb = *d >> 4; \
   lo |= t[ lonyb ]; hi |= t[ hinyb ]; d += pstep;

   p = src; pstep = srcstep;
   extract( p, ltab0 )
   extract( p, ltab1 )
   extract( p, ltab2 )
   extract( p, ltab3 )
   extract( p, ltab4 )
   extract( p, ltab5 )
   extract( p, ltab6 )
   extract( p, ltab7 )

#define unpack( d, w ) \
   *d = ( w >> 24 ) & 0xFF; d += pstep; \
   *d = ( w >> 16 ) & 0xFF; d += pstep; \
   *d = ( w >>  8 ) & 0xFF; d += pstep; \
   *d = w & 0xFF;

   p = dst; pstep = dststep;
   unpack( p, hi )
   p += pstep;
   unpack( p, lo )
}