Introduce GENVALUE(msb, lsb, value) macro to ease dealing with continuous bitfields, just as BIT(x) does for single bits.
GENVALUE_ULL(msb, lsb, value) macro is also added. This is useful mostly for creating values to be packed together via OR operations, ex: u32 val = 0x11110000; val |= GENVALUE(19, 12, 0x5a); now 'val = 0x1115a000' Signed-off-by: Sebastian Frias <s...@laposte.net> Link: https://marc.info/?l=linux-kernel&m=148094498711000&w=2 --- Change in v2: - rename the macro to GENVALUE as proposed by Linus - longer comment attempts to show use case for the macro as proposed by Borislav Change in v3: - use BUILD_BUG_ON_ZERO() to break if some input parameters (essentially 'lsb' but also 'msb') are not constants as proposed by Linus. Indeed, 'lsb' is used twice so it cannot have side-effects; 'msb' is subjected to same constraints for consistency. --- include/linux/bitops.h | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/include/linux/bitops.h b/include/linux/bitops.h index a83c822..419529a0 100644 --- a/include/linux/bitops.h +++ b/include/linux/bitops.h @@ -24,6 +24,31 @@ #define GENMASK_ULL(h, l) \ (((~0ULL) << (l)) & (~0ULL >> (BITS_PER_LONG_LONG - 1 - (h)))) +#ifdef __KERNEL__ +/* + * Equivalent of BIT(x) but for contiguous bitfields + * GENVALUE(1, 0,0xff) = 0x00000003 + * GENVALUE(3, 0,0xff) = 0x0000000f + * GENVALUE(15,8,0xff) = 0x0000ff00 + * GENVALUE(6, 6, 1) = 0x00000040 == BIT(6) + */ +#define GENVALUE(msb, lsb, val) \ + ( \ + /* BUILD_BUG_ON_ZERO() evaluates to 0 */ \ + BUILD_BUG_ON_ZERO(!__builtin_constant_p(msb)) | \ + BUILD_BUG_ON_ZERO(!__builtin_constant_p(lsb)) | \ + (((val) << (lsb)) & (GENMASK((msb), (lsb)))) \ + ) + +#define GENVALUE_ULL(msb, lsb, val) \ + ( \ + /* BUILD_BUG_ON_ZERO() evaluates to 0 */ \ + BUILD_BUG_ON_ZERO(!__builtin_constant_p(msb)) | \ + BUILD_BUG_ON_ZERO(!__builtin_constant_p(lsb)) | \ + (((val) << (lsb)) & (GENMASK_ULL((msb), (lsb)))) \ + ) +#endif + extern unsigned int __sw_hweight8(unsigned int w); extern unsigned int __sw_hweight16(unsigned int w); extern unsigned int __sw_hweight32(unsigned int w); -- 1.8.3.1
