On Sun, 12 Feb 2012, Jeff Epler wrote:
> Date: Sun, 12 Feb 2012 21:31:36 -0600
> From: Jeff Epler <jep...@unpythonic.net>
> Reply-To: EMC developers <emc-developers@lists.sourceforge.net>
> To: EMC developers <emc-developers@lists.sourceforge.net>
> Subject: Re: [Emc-developers] SSERIAL bug with stream type data with
> datawidth=32
>
> On Sun, Feb 12, 2012 at 06:29:49PM -0800, Peter C. Wallace wrote:
>> 147 case 0x06: // byte stream
>> 148 buff = *pin->u32_pin & ((1 << conf->DataLength) - 1);
>> 149 break;
>
> Hm, perhaps this is the correct replacement:
> buff = *pin->u32_pin & (0xffffffffu >> (32 - conf->DataLength));
>
> I wrote the following program to verify the equivalence of this and the
> original-with-special-case for arguments of 1..32 inclusive:
>
> #include <assert.h>
> #include <stdint.h>
>
> uint32_t f1(int n) {
> if(n == 32) return 0xffffffffu;
> return (1 << n) - 1;
> }
>
> uint32_t f2(int n) {
> return 0xffffffffu >> (32 - n);
> }
>
> int main() {
> int i;
> for(i=1; i<32; i++) {
> assert(f1(i) == f2(i));
> }
> return 0;
> }
>
> this moves the "shift 32 bits" case to correspond to a DataLength of 0, which
> probably represents misconfiguration.
>
> Jeff
Thanks! Thats a lot more elegant than what I did...
>
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Peter Wallace
Mesa Electronics
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