Subject: Re: [PATCH] Properly align memory allocations and temporary buffers

From: Junio C Hamano <[email-masked]>
Date: Thu, 06 Jan 2022 16:10:21 -0800

Jessica Clarke <[email-masked]> writes:

> This is also true of uint128_t, it doesn’t fit in a uintmax_t either.

uintmax_t is supposed to be an unsigned integer type capable of
representing any value of any unsigned integer type, so if you have
128-bit unsigned integer, your uintmax_t should be at last that
wide, or your uintmax_t is not uintmax_t as far as C standard is
concerned, no?

uintptr_t is an unsigned integer type that any valid pointer to void
can be converted to this type, then converted back to pointer to
void, and the result will compare equal to the original pointer.  So
the value of uintptr_t cannot be represented by uintmax_t, there is
something wrong.

> uintmax_t was a mistake as it becomes part of the ABI and can never be
> revised even when new integer types come along. uintmax_t can hold any
> valid address, but will strip the metadata.

It is a flaw in the implementation of uintmax_t on the architecture
that needs "the metadata", no?  If the implementation supports a
notion of uintptr_t (i.e. there exists an unsigned integer type that
can safely go back and forth from pointer to void), an unsigned
integer type that is at least as wide as any unsigned integer type
should certainly be able to hold what would fit in uintptr_t, no?

Puzzled.