mirror of
https://github.com/JakeHillion/drgn.git
synced 2024-12-22 17:23:06 +00:00
87b7292aa5
drgn is currently licensed as GPLv3+. Part of the long term vision for drgn is that other projects can use it as a library providing programmatic interfaces for debugger functionality. A more permissive license is better suited to this goal. We decided on LGPLv2.1+ as a good balance between software freedom and permissiveness. All contributors not employed by Meta were contacted via email and consented to the license change. The only exception was the author of commitc4fbf7e589("libdrgn: fix for compilation error"), who did not respond. That commit reverted a single line of code to one originally written by me in commit640b1c011d("libdrgn: embed DWARF index in DWARF info cache"). Signed-off-by: Omar Sandoval <osandov@osandov.com>
153 lines
3.7 KiB
C
153 lines
3.7 KiB
C
// Copyright (c) Meta Platforms, Inc. and affiliates.
|
|
// SPDX-License-Identifier: LGPL-2.1-or-later
|
|
|
|
/**
|
|
* @file
|
|
*
|
|
* Bitwise operations.
|
|
*
|
|
* See @ref BitwiseOperations.
|
|
*/
|
|
|
|
#ifndef DRGN_BITOPS_H
|
|
#define DRGN_BITOPS_H
|
|
|
|
#include "pp.h"
|
|
|
|
/**
|
|
* @ingroup Internals
|
|
*
|
|
* @defgroup BitwiseOperations Bitwise operations
|
|
*
|
|
* Generic bitwise operations.
|
|
*
|
|
* @{
|
|
*/
|
|
|
|
/**
|
|
* Count Trailing Zero bits.
|
|
*
|
|
* Return the number of trailing least significant 0-bits in @p x. This is
|
|
* undefined if @p x is zero.
|
|
*
|
|
* ```
|
|
* ctz(1) == ctz(0b1) == 0
|
|
* ctz(2) == ctz(0b10) == 1
|
|
* ctz(12) == ctz(0b1100) == 2
|
|
* ```
|
|
*
|
|
* @param[in] x Integer.
|
|
*/
|
|
#define ctz(x) generic_bitop(x, PP_UNIQUE(_x), builtin_bitop_impl, ctz)
|
|
|
|
/**
|
|
* Find Last Set bit.
|
|
*
|
|
* Return the one-based index of the most significant 1-bit of @p x or 0 if @p x
|
|
* is 0.
|
|
*
|
|
* ```
|
|
* fls(0) == fls(0b0) == 0
|
|
* fls(1) == fls(0b1) == 1
|
|
* fls(13) == fls(0b1101) == 4
|
|
* ```
|
|
*
|
|
* For unsigned integers,
|
|
* ```
|
|
* fls(x) = floor(log2(x)) + 1, if x > 0
|
|
* 0, if x == 0
|
|
* ```
|
|
*
|
|
* @param[in] x Integer.
|
|
*/
|
|
#define fls(x) generic_bitop(x, PP_UNIQUE(_x), fls_impl,)
|
|
/** @cond */
|
|
/*
|
|
* The straightfoward implementation is bits - clz. However, as noted by the
|
|
* folly implementation: "If X is a power of two, X - Y = 1 + ((X - 1) ^ Y).
|
|
* Doing this transformation allows GCC to remove its own xor that it adds to
|
|
* implement clz using bsr."
|
|
*
|
|
* This doesn't do the normal macro argument safety stuff because it should only
|
|
* be used via generic_bitop() which already does it.
|
|
*/
|
|
#define fls_impl(arg, suffix, x) \
|
|
(x ? 1 + ((8 * sizeof(0u##suffix) - 1) ^ __builtin_clz##suffix(x)) : 0)
|
|
|
|
#define builtin_bitop_impl(arg, suffix, x) __builtin_##arg##suffix(x)
|
|
#define generic_bitop(x, unique_x, impl, impl_arg) ({ \
|
|
__auto_type unique_x = (x); \
|
|
_Static_assert(sizeof(unique_x) <= sizeof(unsigned long long), \
|
|
"type is too large"); \
|
|
(unsigned int)(sizeof(unique_x) <= sizeof(unsigned int) ? \
|
|
impl(impl_arg, , unique_x) : \
|
|
sizeof(unique_x) <= sizeof(unsigned long) ? \
|
|
impl(impl_arg, l, unique_x) : \
|
|
impl(impl_arg, ll, unique_x)); \
|
|
})
|
|
/** @endcond */
|
|
|
|
/**
|
|
* Return whether @p x is a power of two.
|
|
*
|
|
* ```
|
|
* is_power_of_two(0) == 0
|
|
* is_power_of_two(1) == 1
|
|
* is_power_of_two(13) == 0
|
|
* is_power_of_two(32) == 1
|
|
* ```
|
|
*
|
|
* @param[in] x Non-negative integer.
|
|
*/
|
|
#define is_power_of_two(x) is_power_of_two_impl(x, PP_UNIQUE(_x))
|
|
/** @cond */
|
|
#define is_power_of_two_impl(x, unique_x) ({ \
|
|
__auto_type unique_x = (x); \
|
|
unique_x && (unique_x & (unique_x - 1)) == 0; \
|
|
})
|
|
/** @endcond */
|
|
|
|
/**
|
|
* Return the smallest power of two greater than or equal to @p x.
|
|
*
|
|
* ```
|
|
* next_power_of_two(0) == 1 // Zero is not a power of two
|
|
* next_power_of_two(1) == 1
|
|
* next_power_of_two(13) == 16
|
|
* ```
|
|
*
|
|
* @param[in] x Non-negative integer.
|
|
*/
|
|
#define next_power_of_two(x) next_power_of_two_impl(x, PP_UNIQUE(_x))
|
|
/** @cond */
|
|
#define next_power_of_two_impl(x, unique_x) ({ \
|
|
__auto_type unique_x = (x); \
|
|
unique_x ? (typeof(unique_x))1 << fls(unique_x - 1) : \
|
|
(typeof(unique_x))1; \
|
|
})
|
|
/** @endcond */
|
|
|
|
/**
|
|
* Iterate over each 1-bit in @p mask.
|
|
*
|
|
* On each iteration, this sets @p i to the zero-based index of the least
|
|
* significant 1-bit in @p mask and clears that bit in @p mask. It stops
|
|
* iterating when @p mask is zero.
|
|
*
|
|
* ```
|
|
* // Outputs 0 2 3
|
|
* unsigned int mask = 13, i;
|
|
* for_each_bit(i, mask)
|
|
* printf("%u ", i);
|
|
* ```
|
|
*
|
|
* @param[out] i Iteration variable name.
|
|
* @param[in,out] mask Integer to iterate over. This is modified.
|
|
*/
|
|
#define for_each_bit(i, mask) \
|
|
while (mask && (i = ctz(mask), mask &= mask - 1, 1))
|
|
|
|
/** @} */
|
|
|
|
#endif /* DRGN_BITOPS_H */
|