-----Original Message----- From: David Brown [mailto:david@xxxxxxxxxxxxxxx] Sent: den 10 augusti 2012 10:45 To: Göran Steen Cc: gcc-help@xxxxxxxxxxx Subject: Re: 16-bit int Could you please not top-post? It makes it very difficult to follow the order of the thread. Remember that some people see these emails in isolation, rather than threaded in an email client. I've re-ordered the mail below. On 10/08/2012 10:35, Göran Steen wrote: > -----Original Message----- From: David Brown > [mailto:david@xxxxxxxxxxxxxxx] Sent: den 10 augusti 2012 10:12 To: > Göran Steen Cc: gcc-help@xxxxxxxxxxx Subject: Re: 16-bit int > > On 10/08/2012 09:15, Göran Steen wrote: >> Thank you for your response. >> >> I want to make sure that my code snippets, if they are compiled and >> run on a machine with 16-bit int, still works. I don't have access to >> such a machine, so I want to compile and run them with 16-bit int on >> my machine that defaults to 32-bit int. Especially the intermediate >> results' size are interesting. What happens if they are truncated to >> 16-bit? >> > > The answer here is simple - #include <stdint.h>, and use types like > int_fast16_t. If intermediary results might need 32 bits, cast to > int_fast32_t as needed. On a target with 32-bit ints, both these > types will normally be 32-bit (though int_fast16_t could theoretically > be 16-bit), and the cast will do nothing. On a target with 16-bit > ints, you will get 16-bit and 32-bit ints respectively. > > This will give you optimal code for all sizes of target ints, while > also being correct on each target. > > mvh., > > David > Thank you for your response. > > Sorry, this will not help. I want to test the snippets, not change > them. Besides, I don't know if the compiler that will be used for the > 16-bit machine will support any of the types you suggest, so I only > want to use standard types. > > BR /göran If you need to test the snippets on different targets, then you need to have compilers and targets available. You still haven't said which target(s) you are using, but unless it is one like the M68k then there are no compiler switches to help you. Note that there is no point in testing anything until you have done what you can to make sure the code is correctly written. Otherwise your tests may work on some targets by coincidence, but not on others, or may be sub-optimal on some targets. Any C99 compiler - and almost all pre-C99 compilers - will have <stdint.h>. I don't know of any compiler less than 15 years old that doesn't come with a <stdint.h>, and many people using such compilers have written their own <stdint.h>. The int_fast16_t and int_fast32_t types (and the unsigned versions) are mandatory in <stdint.h>, so you can take it for granted that /all/ compilers support them. This is unlike the fixed-size types (like int16_t) that will be defined if and only if the target supports types of exactly that size (some architectures don't support the smaller types). mvh., David Thank you for your response. I want to test the snippets with 16-bit int, without having target system or compiler available. You wrote that there is no compiler switch to help me. Thank you for that answer. BR /göran
