Hi Michael, Thank you a lot for your message... however I must admit my complete ignorance (and lack of practice) of the whole C++ / templating world. I mean that I cannot understand (yet) your template version - such a shame ; nor adapt it to this fix. Just if you have a few minutes to enlighten me : if we were to look at the proposed patch here https://github.com/openvehicles/Open-Vehicle-Monitoring-System-3/pull/736/fi... ; and if we would introduce your template implementation, how should we rewrite the "patched" version to make use of this implementation ? result.Cast((uint32_t)SIGNEX(val, m_signal_size-1), DBC_NUMBER_INTEGER_SIGNED); (my naïve attempts all failed compilation with all sorts of "error: use of 'this' in a constant expression" and "error: no matching function for call to 'sign_extend(uint64_t&)'" so a little help would be appreciated) Additionally, could you please expand a little on the benefits it adds - you're talking about type-safety, if you could just illustrate it in this context ? Sorry for being ignorant on this subject. Regards, Ludovic Le 14/10/2022 à 10:40, Michael Geddes a écrit :
OOH.. nice one. I had missed that in my template implementation. I'm a big fan of using C++ templating to do type-safe versions of this kind of stuff... This is my template version: /** Sign extend an unsigned to a signed integer of the same size. */ template<typename UINT, typename INT, uint8_t SIGNBIT> INT sign_extend( UINT uvalue) { typedef typename std::make_unsigned<INT>::type uint_t; uint_t newuvalue = uvalue; if ( newuvalue & ( UINT(1U) << SIGNBIT) ) { newuvalue |= ~((uint_t(1U) << SIGNBIT) - 1); } return reinterpret_cast<INT &>(uvalue); } It could probably be converted into a version that would infer some of the types.. but this should work pretty well and should compile down to close to the same code. Usage from my code: Where BYTES is a templated integer value parameter. res = sign_extend < uint32_t, int32_t, BYTES * 8 - 1 > (ures);
I also have a templated buffer extractor that allows for checking available space! For example this code (which extracts 2 bytes as a signed integer), which should now work with sign extension thanks to your bugfix and the above templated version of sign extension:
int32_t signedValue; if (!can_buff_int<2>(data, 10, signedValue )) { ESP_LOGE(TAG, "IoniqISOTP.BMC: BMS Current: Bad Buffer"); } else { StdMetrics.ms_v_bat_current->SetValue((float)signedValue / 10.0, Amps); }
//.ichael
On Fri, 14 Oct 2022 at 05:35, Ludovic LANGE <ll-ovmsdev@lange.nom.fr> wrote:
Dear list,
I've come across an issue with the DBC parser where a non-32-bit negative number was incorrectly decoded.
I've traced this to an issue with sign-extension ; and I've proposed a fix here https://github.com/openvehicles/Open-Vehicle-Monitoring-System-3/pull/736
Before having it merged, I'd like to gather some feedback from users of the DBC module.
Please have a look, and comment directly on the GitHub PR.
Thanks in advance !
Regards,
Ludovic
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