BitPage.hpp

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#ifndef BIT_PAGE_HPP
#define BIT_PAGE_HPP
 
#include <cassert>
#include "BitTag.hpp"
 
namespace moab
{
 
class Range;
 
/**\brief bit tag data
 *
 * This class represents a fixed-size block of memory in which bit tag
 * values are stored.
 */
class BitPage
{
 public:
 /**\brief Initialize memory
 *
 *\param bits_per_ent Number of bits in each tag value.
 * MUST BE A POWER OF TWO.
 *\param init_val The lower bits_per_ent bits of this byte are
 * used to initialize each tag value.
 */
 BitPage( int bits_per_ent, unsigned char init_val );
 
 /**\brief Get tag values
 *
 * Get 'count' tag values, beginning with the one at 'offset'.
 *\param offset Offset into list of values, where a value of zero indicates
 * the first tag value, a value of one indicates the second
 * tag value, etc. NOTE: This is the value offset, not the
 * bit offset.
 *\param count Number of consecutive tag values to get.
 *\param bits_per_ent Number of bits composing each tag value.
 * NOTE: Must be a power of two.
 *\param data Memory into which to copy tag values. Each value is copied
 * into a separate byte, such that the lower bits of the bit
 * contain the tag value and any unused higher bits are zero.
 */
 void get_bits( int offset, int count, int bits_per_ent, unsigned char* data ) const;
 
 /**\brief Set tag values
 *
 * Set 'count' tag values, beginning with the one at 'offset'.
 *\param offset Offset into list of values, where a value of zero indicates
 * the first tag value, a value of one indicates the second
 * tag value, etc. NOTE: This is the value offset, not the
 * bit offset.
 *\param count Number of consecutive tag values to set.
 *\param bits_per_ent Number of bits composing each tag value.
 * NOTE: Must be a power of two.
 *\param data Memory from which to copy tag values. Each value is copied
 * from a separate byte. The lower 'bits_per_ent' of each
 * byte are used as the tag value. Any additional higher bits
 * are ignored.
 */
 void set_bits( int offset, int count, int bits_per_ent, const unsigned char* data );
 
 /**\brief Set several tag values to the same value.
 *
 * Set 'count' tag values to specified value.
 *\param offset Offset into list of values, where a value of zero indicates
 * the first tag value, a value of one indicates the second
 * tag value, etc. NOTE: This is the value offset, not the
 * bit offset.
 *\param count Number of consecutive tag values to set.
 *\param bits_per_ent Number of bits composing each tag value.
 * NOTE: Must be a power of two.
 *\param value The lower 'bits_per_ent' of this
 * byte are used as the tag value. Any additional higher bits
 * are ignored.
 */
 void set_bits( int offset, int count, int bits_per_ent, unsigned char value );
 
 /**\brief Get tag value
 *
 * Get one tag value.
 *\param offset Offset into list of values, where a value of zero indicates
 * the first tag value, a value of one indicates the second
 * tag value, etc. NOTE: This is the value offset, not the
 * bit offset.
 *\param bits_per_ent Number of bits composing each tag value.
 * NOTE: Must be a power of two.
 *\return A byte containing the tag value in the lower bits with
 * any unused higher bits zeroed.
 */
 unsigned char get_bits( int offset, int bits_per_ent ) const;
 
 /**\brief Set tag value
 *
 * Set tag value.
 *\param offset Offset into list of values, where a value of zero indicates
 * the first tag value, a value of one indicates the second
 * tag value, etc. NOTE: This is the value offset, not the
 * bit offset.
 *\param bits_per_ent Number of bits composing each tag value.
 * NOTE: Must be a power of two.
 *\param value The lower 'bits_per_ent' of this
 * byte are used as the tag value. Any additional higher bits
 * are ignored.
 */
 void set_bits( int offset, int bits_per_ent, unsigned char data );
 
 /**\brief Search stored values for specified value.
 *
 * Find the offsets n in the data at which the specified value occurs,
 * and for each one insert 'start + n' into the passed Range.
 *\param value The value to look for
 *\param offset The offset at which to begin searching
 *\param count The number of values to search
 *\param bits_per_ent Number of bits composing each tag value.
 *\param results Result list.
 *\param start The handle of the entity corresponding to the
 * tag value stored at 'offset'
 */
 void search( unsigned char value, int offset, int count, int bits_per_ent, Range& results, EntityHandle start )
 const;
 
 private:
 /**\brief The actual array of bytes */
 char byteArray[BitTag::PageSize];
};
 
inline unsigned char BitPage::get_bits( int offset, int per_ent ) const
{
 // Assume per_ent is a power of two, which should be guaranteed
 // by higher-level code.
 unsigned char mask = (unsigned char)( 1 << per_ent ) - 1; // 2^per_ent - 1
 int byte = ( offset * per_ent ) >> 3; // shifting 3 is dividing by eight
 int bit = ( offset * per_ent ) & 7; // masking with 7 is modulo eight
 assert( byte < BitTag::PageSize );
 return (unsigned char)( byteArray[byte] >> bit ) & mask;
}
 
inline void BitPage::set_bits( int offset, int per_ent, unsigned char bits )
{
 int byte = ( offset * per_ent ) >> 3; // shifting 3 is dividing by eight
 int bit = ( offset * per_ent ) & 7; // masking with 7 is modulo eight
 assert( byte < BitTag::PageSize );
 // Assume per_ent is a power of two, which should be guaranteed
 // by higher-level code.
 unsigned char mask = (unsigned char)( ( 1 << per_ent ) - 1 ) << bit;
 byteArray[byte] = (char)( ( byteArray[byte] & ~mask ) | ( ( bits << bit ) & mask ) );
}
 
inline void BitPage::get_bits( int offset, int count, int per_ent, unsigned char* data ) const
{
 unsigned char* end = data + count;
 while( data != end )
 *( data++ ) = get_bits( offset++, per_ent );
}
 
inline void BitPage::set_bits( int offset, int count, int per_ent, const unsigned char* data )
{
 const unsigned char* end = data + count;
 while( data != end )
 set_bits( offset++, per_ent, *( data++ ) );
}
 
inline void BitPage::set_bits( int offset, int count, int per_ent, unsigned char value )
{
 int end = offset + count;
 while( offset < end )
 set_bits( offset++, per_ent, value );
}
 
} // namespace moab
 
#endif