From 293185e71e33274610e8b5801f7f41ff0c620edd Mon Sep 17 00:00:00 2001 From: Rob Landley Date: Wed, 26 May 2021 04:29:30 -0500 Subject: Better link to LP64 documentation. --- www/design.html | 40 +++++++++++++++++++++------------------- 1 file changed, 21 insertions(+), 19 deletions(-) (limited to 'www') diff --git a/www/design.html b/www/design.html index e6519135..dbe7858c 100644 --- a/www/design.html +++ b/www/design.html @@ -342,22 +342,21 @@ corner cases.

32/64 bit

Toybox should work on both 32 bit and 64 bit systems. 64 bit desktop -hardware went mainstream in 2005 and was essentially ubiquitous -by the end of the decade, but 32 bit hardware will continue to be important -in embedded devices for several more years.

- -

Toybox relies on the fact that on any Unix-like platform, pointer and long -are always the same size (on both 32 and 64 bit). Pointer and int are _not_ -the same size on 64 bit systems, but pointer and long are. -This is guaranteed by the LP64 memory model, a Unix standard (which Linux -and MacOS X both implement, and which modern 64 bit processors such as -x86-64 were designed for).

- -

Back -before unix.org went down, they hosted the -LP64 standard and -the LP64 rationale, but the important part is -LP64 gives all the basic C integer types defined sizes:

+hardware went mainstream in in 2005 +and was essentially ubiquitous by 2012, +but 32 bit hardware will continue to be important in embedded devices for years to come.

+ +

Toybox relies on the +LP64 standard +which Linux, MacOS X, and BSD all implement, and which modern 64 bit processors such as +x86-64 were explicitly designed to +support. (Here's the original LP64 white paper.)

+ +

LP64 defines explicit sizes for all the basic C integer types, and +guarantees that on any Unix-like platform "long" and "pointer" types +are always the same size. This means it's safe to assign pointers into +longs and vice versa without losing data: on 32 bit systems both are 32 bit, +on 64 bit systems both are 64 bit.

@@ -368,9 +367,12 @@ LP64 gives all the basic C integer types defined sizes:

C type32 bit
sizeof		64 bit
sizeof
long long8 bytes8 bytes
-

Note that Windows doesn't work like this, and I don't care. -The -insane legacy reasons why this is broken on Windows are explained here.

+

LP64 eliminates the need to use c99 "uint32_t" and friends: the basic +C types all have known size/behavior, and the only type whose +size varies is "long", which is the natural register size of the processor.

+ +

(Note that Windows doesn't work like this, and I don't care, but if you're +curious here are The insane legacy reasons why this is broken on Windows are explained here.

Signedness of char

On platforms like x86, variables of type char default to unsigned. On -- cgit v1.2.3