**diff options**

author | David Howells <dhowells@redhat.com> | 2012-09-13 13:09:33 +0100 |
---|---|---|

committer | Rusty Russell <rusty@rustcorp.com.au> | 2012-10-08 13:50:11 +1030 |

commit | aacf29bf1bf133f6219e6f8969d4ebc2ac76458f (patch) | |

tree | b4379ab6617d1e963020365e03cda0b551bc3237 /include | |

parent | cf7f601c067994f371ba77721d1e45fce61a4569 (diff) |

MPILIB: Provide count_leading/trailing_zeros() based on arch functions

Provide count_leading/trailing_zeros() macros based on extant arch bit scanning
functions rather than reimplementing from scratch in MPILIB.
Whilst we're at it, turn count_foo_zeros(n, x) into n = count_foo_zeros(x).
Also move the definition to asm-generic as other people may be interested in
using it.
Signed-off-by: David Howells <dhowells@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
Cc: Arnd Bergmann <arnd@arndb.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Diffstat (limited to 'include')

-rw-r--r-- | include/asm-generic/bitops/count_zeros.h | 57 |

1 files changed, 57 insertions, 0 deletions

diff --git a/include/asm-generic/bitops/count_zeros.h b/include/asm-generic/bitops/count_zeros.h new file mode 100644 index 00000000000..97520d21fe6 --- /dev/null +++ b/include/asm-generic/bitops/count_zeros.h @@ -0,0 +1,57 @@ +/* Count leading and trailing zeros functions + * + * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved. + * Written by David Howells (dhowells@redhat.com) + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public Licence + * as published by the Free Software Foundation; either version + * 2 of the Licence, or (at your option) any later version. + */ + +#ifndef _ASM_GENERIC_BITOPS_COUNT_ZEROS_H_ +#define _ASM_GENERIC_BITOPS_COUNT_ZEROS_H_ + +#include <asm/bitops.h> + +/** + * count_leading_zeros - Count the number of zeros from the MSB back + * @x: The value + * + * Count the number of leading zeros from the MSB going towards the LSB in @x. + * + * If the MSB of @x is set, the result is 0. + * If only the LSB of @x is set, then the result is BITS_PER_LONG-1. + * If @x is 0 then the result is COUNT_LEADING_ZEROS_0. + */ +static inline int count_leading_zeros(unsigned long x) +{ + if (sizeof(x) == 4) + return BITS_PER_LONG - fls(x); + else + return BITS_PER_LONG - fls64(x); +} + +#define COUNT_LEADING_ZEROS_0 BITS_PER_LONG + +/** + * count_trailing_zeros - Count the number of zeros from the LSB forwards + * @x: The value + * + * Count the number of trailing zeros from the LSB going towards the MSB in @x. + * + * If the LSB of @x is set, the result is 0. + * If only the MSB of @x is set, then the result is BITS_PER_LONG-1. + * If @x is 0 then the result is COUNT_TRAILING_ZEROS_0. + */ +static inline int count_trailing_zeros(unsigned long x) +{ +#define COUNT_TRAILING_ZEROS_0 (-1) + + if (sizeof(x) == 4) + return ffs(x); + else + return (x != 0) ? __ffs(x) : COUNT_TRAILING_ZEROS_0; +} + +#endif /* _ASM_GENERIC_BITOPS_COUNT_ZEROS_H_ */ |