While type punning through unions is allowed in C, the only way which works in both C and C++ (without breaking the strict aliasing rule) is using memcpy. In such case, the call to memcpy will completely optimized away by every decent compiler.
Gesendet: Samstag, 06. April 2019 um 11:28 Uhr Von: "cyrille henry" ch@chnry.net An: "pd-list@lists.iem.at" pd-list@lists.iem.at Betreff: Re: [PD] Getting 32 bit floating point number from 4 sequential bytes
hello, I think a better way (that did not need to copy the data) is to use a union : i.e. 2 different type can be declared in the same memory space. something like :
// union type definition union int_and_float { int8_t my_int[4]; float my_float; };
int_and_float my_int_and_float; // declaration of a variable of this type
my_int_and_float.my_int[0] = 0; // value assignation my_int_and_float.my_int[1] = 0; my_int_and_float.my_int[2] = 0; my_int_and_float.my_int[3] = 0;
the float data should be in : my_int_and_float.my_float;
I did not test this code, It will certainly contain syntaxes errors, but you'll find the way to correct it on internet...
An other solution is to use bitwise operator :
my_float = (byte1 << 24) & (byte2 << 16) & (byte3 << 8) & byte4;
cheers Cyrille
Le 05/04/2019 à 19:04, Arda Eden a écrit :
I found a method using "memcpy". Seems like it is working for now.
Arda Eden <ardaeden@gmail.com mailto:ardaeden@gmail.com>, 5 Nis 2019 Cum, 16:00 tarihinde şunu yazdı:
Hi, I am trying to write a Pure Data external for getting real time motion capture values from an Xsens system. According to the manual (https://xsens.com/download/usermanual/3DBM/MVN_real-time_network_streaming_protocol_specification.pdf), the x, y and z coordinates of the skeleton segment positions are transferred over network (udp) as sequential 4 bytes (32 bit floating point - big endian). I am reading the udp data with [netreceive] succesfully and able to reach any value I need. Now trying to find a way to combine these (big endian) sequential 4 bytes in order to get the resulting 32 bit floating point number. A little advice would speed me up. By the way, I studied the [oscparse] source. It was very helpful in most ways but also a little complicated too. Thanks already. -- Arda EDEN Yıldız Teknik Üniversitesi Sanat ve Tasarım Fakültesi Müzik ve Sahne Sanatları Bölümü Duysal (Ses) Sanatları Tasarımı Programı İstanbul/Türkiye Yildiz Technical University Faculty of Art and Design Department of Music and Performing Arts Audio Design Program Istanbul/Turkey-- Arda EDEN Yıldız Teknik Üniversitesi Sanat ve Tasarım Fakültesi Müzik ve Sahne Sanatları Bölümü Duysal (Ses) Sanatları Tasarımı Programı İstanbul/Türkiye
Yildiz Technical University Faculty of Art and Design Department of Music and Performing Arts Audio Design Program Istanbul/Turkey
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