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bitfield.h

/*
 *    FILE        bitfield.h
 *
 *    Version     1.1
 *    Author      Copyright (c) Marc A. Viredaz, 1998
 *                DEC Western Research Laboratory, Palo Alto, CA
 *    Date        April 1998 (April 1997)
 *    System      Advanced RISC Machine (ARM)
 *    Language    C or ARM Assembly
 *    Purpose     Definition of macros to operate on bit fields.
 */



#ifndef __BITFIELD_H
#define __BITFIELD_H

#ifndef __ASSEMBLY__
#define UData(Data)     ((unsigned long) (Data))
#else
#define UData(Data)     (Data)
#endif


/*
 * MACRO: Fld
 *
 * Purpose
 *    The macro "Fld" encodes a bit field, given its size and its shift value
 *    with respect to bit 0.
 *
 * Note
 *    A more intuitive way to encode bit fields would have been to use their
 *    mask. However, extracting size and shift value information from a bit
 *    field's mask is cumbersome and might break the assembler (255-character
 *    line-size limit).
 *
 * Input
 *    Size        Size of the bit field, in number of bits.
 *    Shft        Shift value of the bit field with respect to bit 0.
 *
 * Output
 *    Fld         Encoded bit field.
 */

#define Fld(Size, Shft) (((Size) << 16) + (Shft))


/*
 * MACROS: FSize, FShft, FMsk, FAlnMsk, F1stBit
 *
 * Purpose
 *    The macros "FSize", "FShft", "FMsk", "FAlnMsk", and "F1stBit" return
 *    the size, shift value, mask, aligned mask, and first bit of a
 *    bit field.
 *
 * Input
 *    Field       Encoded bit field (using the macro "Fld").
 *
 * Output
 *    FSize       Size of the bit field, in number of bits.
 *    FShft       Shift value of the bit field with respect to bit 0.
 *    FMsk        Mask for the bit field.
 *    FAlnMsk     Mask for the bit field, aligned on bit 0.
 *    F1stBit     First bit of the bit field.
 */

#define FSize(Field)    ((Field) >> 16)
#define FShft(Field)    ((Field) & 0x0000FFFF)
#define FMsk(Field)     (((UData (1) << FSize (Field)) - 1) << FShft (Field))
#define FAlnMsk(Field)  ((UData (1) << FSize (Field)) - 1)
#define F1stBit(Field)  (UData (1) << FShft (Field))


/*
 * MACRO: FInsrt
 *
 * Purpose
 *    The macro "FInsrt" inserts a value into a bit field by shifting the
 *    former appropriately.
 *
 * Input
 *    Value       Bit-field value.
 *    Field       Encoded bit field (using the macro "Fld").
 *
 * Output
 *    FInsrt      Bit-field value positioned appropriately.
 */

#define FInsrt(Value, Field) \
                  (UData (Value) << FShft (Field))


/*
 * MACRO: FExtr
 *
 * Purpose
 *    The macro "FExtr" extracts the value of a bit field by masking and
 *    shifting it appropriately.
 *
 * Input
 *    Data        Data containing the bit-field to be extracted.
 *    Field       Encoded bit field (using the macro "Fld").
 *
 * Output
 *    FExtr       Bit-field value.
 */

#define FExtr(Data, Field) \
                  ((UData (Data) >> FShft (Field)) & FAlnMsk (Field))


#endif /* __BITFIELD_H */

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