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authorMatthijs Kooijman <matthijs@stdin.nl>2014-02-18 18:11:22 +0100
committerMatthijs Kooijman <matthijs@stdin.nl>2014-02-19 16:09:29 +0100
commitf76c327aae447ca595a428c6783d817ec2f23ed9 (patch)
treee316b50001129bb9757216ff65a9ab953dbb7f2e /bootloaders/stk500v2/STK500V2.pnps
parentf4cd0ff0a4708b94744e08bbd72ce389797b93a8 (diff)
Use a union in IPAddress for uint8_t[] <-> uint32_t conversion
Previously, pointer casting was used, but this resulted in strict-aliasing warnings: IPAddress.h: In member function ‘IPAddress::operator uint32_t() const’: IPAddress.h:46:61: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing] operator uint32_t() const { return *((uint32_t*)_address); }; ^ IPAddress.h: In member function ‘bool IPAddress::operator==(const IPAddress&) const’: IPAddress.h:47:81: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing] bool operator==(const IPAddress& addr) const { return (*((uint32_t*)_address)) == (*((uint32_t*)addr._address)); }; ^ IPAddress.h:47:114: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing] bool operator==(const IPAddress& addr) const { return (*((uint32_t*)_address)) == (*((uint32_t*)addr._address)); }; Converting between unrelated types like this is commonly done using a union, which do not break the strict-aliasing rules. Using that union, inside IPAddress there is now an attribute _address.bytes for the raw byte arra, or _address.dword for the uint32_t version. Since we now have easy access to the uint32_t version, this also removes two memcpy invocations that can just become assignments. This patch does not change the generated code in any way, the compiler already optimized away the memcpy calls and the previous casts mean exactly the same. This is a different implementation of a part of #1399 and it helps toward fixing #1728.
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