Re: [RFC][PATCH] new byteorder primitives - ..._{replace,get}_bits()
flat view
From: Al Viro <viro@ZenIV.linux.org.uk>
Date: 2017-12-12 23:49:03
Also in:
lkml
Subsystem:
the rest · Maintainer:
Linus Torvalds
On Tue, Dec 12, 2017 at 12:04:09PM -0800, Jakub Kicinski wrote:
quoted
static __always_inline u64 mask_to_multiplier(u64 mask) { return mask & (mask ^ (mask - 1)); }
D'oh. Even simpler than that, of course -
static __always_inline u64 mask_to_multiplier(u64 mask)
{
return mask & -mask;
}
Very nice! The compilation-time check if the value can fit in a field covered by the mask (if they're both known) did help me catch bugs early a few times over the years, so if it could be preserved we can maybe even drop the FIELD_* macros and just use this approach?
Umm... Something like this, perhaps? Same bunch, plus u{16,32,64}_...
variants for host-endian. Adding sanity check on mask is also not
hard, but I don't know how useful it actually is...
diff --git a/include/linux/byteorder/generic.h b/include/linux/byteorder/generic.h
index 451aaa0786ae..a032de9aa03d 100644
--- a/include/linux/byteorder/generic.h
+++ b/include/linux/byteorder/generic.h@@ -187,4 +187,36 @@ static inline void be32_to_cpu_array(u32 *dst, const __be32 *src, size_t len) dst[i] = be32_to_cpu(src[i]); } +extern void __compiletime_error("value doesn't fit into mask") +__field_overflow(void); +static __always_inline u64 mask_to_multiplier(u64 mask) +{ + return mask & -mask; +} + +#define ____MAKE_OP(type,base,to,from) \ +static __always_inline __##type type##_replace_bits(__##type old, \ + base val, base mask) \ +{ \ + __##type m = to(mask); \ + if (__builtin_constant_p(val) && \ + (val & ~(mask/mask_to_multiplier(mask)))) \ + __field_overflow(); \ + return (old & ~m) | \ + (to(val * mask_to_multiplier(mask)) & m); \ +} \ +static __always_inline base type##_get_bits(__##type v, base mask) \ +{ \ + return (from(v) & mask)/mask_to_multiplier(mask); \ +} +#define __MAKE_OP(size) \ + ____MAKE_OP(le##size,u##size,cpu_to_le##size,le##size##_to_cpu) \ + ____MAKE_OP(be##size,u##size,cpu_to_be##size,be##size##_to_cpu) \ + ____MAKE_OP(u##size,u##size,,) +__MAKE_OP(16) +__MAKE_OP(32) +__MAKE_OP(64) +#undef __MAKE_OP +#undef ____MAKE_OP + #endif /* _LINUX_BYTEORDER_GENERIC_H */