In an Open Source program I wrote, I'm reading binary data (written by another program) from a file and outputting ints, doubles, and other assorted data types. One of the challenges is that it needs to run on 32-bit and 64-bit machines of both endiannesses, which means that I end up having to do quite a bit of low-level bit-twiddling. ...
I'm curious about conventions for type-punning pointers/arrays in C++. Here's the use case I have at the moment: Compute a simple 32-bit checksum over a binary blob of data by treating it as an array of 32-bit integers (we know its total length is a multiple of 4), and then summing up all values and ignoring overflow. I would expect...
I'm working with HiTech PICC32 on the PIC32MX series of microprocessors, but I think this question is general enough for anyone knowledgable in C. (This is almost equivalent to C90, with sizeof(int) = sizeof(long) = sizeof(float) = 4.) Let's say I read a 4-byte word of data that represents a float. I can quickly convert it to its actual...
Hello, everyone! I need to be able to convert byte arrays to/from other primitive type arrays, but instead of casting, I need type punning. Correct term for raw copy without casting? I thought it would be possible to do the following: // idea: byte[12] -> int[3], and int[3] -> byte[12] int[] ints; ByteBuffer bb = ByteBuffer.wrap( ...
I have used unions earlier comfortably; today I was alarmed when I read this post and came to know that this code union ARGB { uint32_t colour; struct componentsTag { uint8_t b; uint8_t g; uint8_t r; uint8_t a; } components; } pixel; pixel.colour = 0xff040201; /* ---- somewhere down the...
I'm writing C for the PIC32MX, compiled with Microchip's PIC32 C compiler (based on GCC 3.4). Added The standard I'm following is GNU99 (C99 with GNU extensions, compiler flag -std=gnu99) My problem is this: I have some reprogrammable numeric data that is stored either on EEPROM or in the program flash of the chip. This means that when...
This code is for Microchip's PIC32MX microprocessor. Their compiler is essentially GCC 3.4. I tend use GCC's __packed__ attribute to pack bitfields into a union, and later retrieve them as an unsigned char (ie. type-punning) for sending over SPI or I2C. This behaviour is all defined by my implementation, and works perfectly. I prefer th...
Hello! Here is function that i am writing on 64 bit linux machine. void myfunc(unsigned char* arr) //array of 8 bytes is passed by reference { unsigned long a = 0; //8 bytes unsigned char* LL = (unsigned char*) &a; LL[0] = arr[6]; LL[1] = arr[3]; LL[2] = arr[1]; LL[3] = arr[7]; LL[4] = arr[5]; LL[5] = arr[4]; ...