mcci_bootloader_bits.h

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/*
 
Module: mcci_bootloader_bits.h
 
Function:
        Bit macros for the MCCI bootloader.
 
Copyright and License:
        This file copyright (C) 2021 by
 
                MCCI Corporation
                3520 Krums Corners Road
                Ithaca, NY  14850
 
        See accompanying LICENSE file for copyright and license information.
 
Author:
        Terry Moore, MCCI Corporation   March 2021
 
*/
 
#ifndef _mcci_bootloader_bits_h_
#define _mcci_bootloader_bits_h_        /* prevent multiple includes */
 
#pragma once
 
#ifdef __cplusplus
extern "C" {
#endif
 
///
/// \brief compute log2 of an power of 2.
///
/// This can be used at compile time or run time.
///
/// \see Knuth V4 7.1.3 (49).
///
#define MCCI_BOOTLOADER_LOG2_POW2(x)                    \
    ((x) == 0 ? -1 :                                    \
     (((x) & 0x5555555555555555u) == 0 ? 1 : 0) +       \
     (((x) & 0x3333333333333333u) == 0 ? 2 : 0) +       \
     (((x) & 0x0f0f0f0f0f0f0f0fu) == 0 ? 4 : 0) +       \
     (((x) & 0x00FF00FF00FF00FFu) == 0 ? 8 : 0) +       \
     (((x) & 0x0000FFFF0000FFFFu) == 0 ? 16 : 0) +      \
     (((x) & 0x00000000FFFFFFFFu) == 0 ? 32 : 0))
 
///
/// \brief get shift count from field mask.
///
/// \param[in] x        field mask; bitmask should be of form 0*11*0*
///
/// \details
///     We might have some 64-bit fields, so...
///     this goes through through bit 63. We use `~(x)+1` to form the unsigned twos-
///     complement of \c x without trying to negate an unsigned or doing
///     a type-cast. Avoids warnings on some compilers.  This is exactly
///     what Knuth calls "rho" (the ruler function).
///
/// \see Knuth V4 7.1.3.
///
#define MCCI_BOOTLOADER_FIELD_SHIFT(x)  MCCI_BOOTLOADER_LOG2_POW2((x) & (~(x)+1))
 
/*! get LSB from field mask */
#define MCCI_BOOTLOADER_FIELD_LSB(fmask)                        \
        ((fmask) & (~(fmask) + 1u))
 
/*! generate field value (properly positioned) */
#define MCCI_BOOTLOADER_VALUE_MAKE_FIELD(val, fmask)            \
        (MCCI_BOOTLOADER_FIELD_LSB(fmask) * (val))
 
/*! generate field value (properly positioned) */
#define MCCI_BOOTLOADER_FIELD_SET_VALUE(fmask, val)             \
        (MCCI_BOOTLOADER_FIELD_LSB(fmask) * (val))
 
/*! extract and normalize value of field */
#define MCCI_BOOTLOADER_VALUE_GET_FIELD(val, fmask)             \
        (((val) & (fmask)) >> MCCI_BOOTLOADER_FIELD_SHIFT(fmask))
 
#ifdef __cplusplus
}
#endif
 
#endif /* _mcci_bootloader_bits_h_ */