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Add a special case where we can derive valid s32 bounds from umin/umax or smin/smax by stitching together negative s32 subrange and non-negative s32 subrange. That requires upper 32 bits to form a [N, N+1] range in u32 domain (taking into account wrap around, so 0xffffffff to 0x00000000 is a valid [N, N+1] range in this sense). See code comment for concrete examples. Eduard Zingerman also provided an alternative explanation ([0]) for more mathematically inclined readers: Suppose: . there are numbers a, b, c . 2**31 <= b < 2**32 . 0 <= c < 2**31 . umin = 2**32 * a + b . umax = 2**32 * (a + 1) + c The number of values in the range represented by [umin; umax] is: . N = umax - umin + 1 = 2**32 + c - b + 1 . min(N) = 2**32 + 0 - (2**32-1) + 1 = 2, with b = 2**32-1, c = 0 . max(N) = 2**32 + (2**31 - 1) - 2**31 + 1 = 2**32, with b = 2**31, c = 2**31-1 Hence [(s32)b; (s32)c] forms a valid range. [0] https://lore.kernel.org/bpf/d7af631802f0cfae20df77fe70068702d24bbd31.camel@gmail.com/ Acked-by: Eduard Zingerman <eddyz87@gmail.com> Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/r/20231102033759.2541186-7-andrii@kernel.org Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.