static const char rcsid[] = "$Header: c:/mctex/imagen/rcs/bset.c 1.1 91/08/05 23:41:24 ROOT_DOS Exp Locker: ROOT_DOS $";

/* Copyright (c) 1993 Neal Becker
 * All rights reserved.
 * Permission to copy for any purpose is hereby granted
 * so long as this copyright notice remains intact.
*/

/*
$Log:	bset.c $
 * Revision 1.1  91/08/05  23:41:24  ROOT_DOS
 * Initial revision
 * 
*/

static const int BitMask[ 8 ] = { 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80 };

inline int min( int a, int b ) {
  return ( a > b ) ? b : a;
}

inline unsigned char TopPart( char S, int Pos ) {
  return ((unsigned char)S) >> Pos;
}

inline unsigned char BottomPart( char S, int Pos ) {
  return S << ( 8 - Pos );
}

static void MemOr( char* D, char* S, int count ) {
  for(; count != 0; count--, D++, S++ )
    *D |= *S;
}

void Bset( char* S, int Slen, char* D, int Dlen, int Pos ) {
  char* Dest = D + ( Pos / 8 );
  int BitPos = Pos % 8;
  char* Dend = D + Dlen - 1;
  int BytesToMove = min( Slen, Dlen - ( Pos / 8 ) );
  if( BitPos == 0 ) {
    MemOr( Dest, S, BytesToMove );
  }
  else {
    for( ; BytesToMove != 0; BytesToMove--, Dest++, S++ ) {
      *Dest |= TopPart( *S, BitPos );
      if( Dest + 1 > Dend ) break;
      *( Dest + 1 ) |= BottomPart( *S, BitPos );
    }
  }
}

void SetBits( int Slen, char* D, int Dlen, int Pos ) {
  char* Dest = D + ( Pos / 8 );
  int BitPos = 7 - (Pos % 8);
  int BitsToMove = min( Slen, Dlen - Pos );
  for( ; BitsToMove > 0 ; BitsToMove-- ) {
    *Dest |= BitMask[ BitPos-- ];
    if( BitPos < 0 ) {
      Dest++;
      BitPos = 7;
    }
  }
}