Hi all, I have been looking at the bitops api for various architectures. I am curious why some architectures define the 'nr' argument as a signed int and some architectures define it as an unsigned int. there are even some architectures (mips, sparc) that mix the prototypes between atomic and non-atomic functions (set_bit and __set_bit). The x86 architecture uses a long as its 'nr' argument. the atomic operations documentation gives a prototype of the bit operations using unsigned int for 'nr'. (https://elixir.bootlin.com/linux/latest/source/Documentation/core-api/atomic_ops.rst#L451) i've looked at the commit where the sparc architecture changes from using signed to unsigned, but the commit message didn't have an explanation on that part of it. (https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8a8b836b91aa170a383f2f360b73d3d23160d9d7) i've dug through the uses of this function and most drivers/kernel subsystems use this to set bits in a status bitfield where the 'nr' argument is a #define. it doesn't seem to matter which type the argument is, but i'm curious why there are different implementations. asm-generic implementation: static inline void __set_bit(int nr, volatile unsigned long *addr) { unsigned long mask = BIT_MASK(nr); unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr); *p |= mask; } sparc implementation: static inline void set_bit(unsigned long nr, volatile unsigned long *addr) { unsigned long *ADDR, mask; ADDR = ((unsigned long *) addr) + (nr >> 5); mask = 1 << (nr & 31); (void) ___set_bit(ADDR, mask); } thank you, wes edens _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
