Some architecture use 64 bits for long type..LP64 convention use 64 bits for long type. Unlike standard longs, unsigned longs will not store negative numbers, making their range from 0 to 4,294,967,295 (2^32 - 1). Printing a uint32_t value with "%u" is non-portable. On Arduino Uno (and equivalent) you have to explicitly cast the calculation when dealing with uint8_t for this to work. If you don’t, the result of the subtraction will become negative if given the right input. Or perhaps there's a better way. Modern programmers should use the standardized explicit-size types instead: uin8_t, int16_t, uint32_t, etc. So it COMMON for char to be 8bits, int to be either 16 or 32, and long to 32. That's a good question. I'm using an unsigned long … Hello, I am trying to modify a library at the moment. int infrared1 = A0; int infrared2 = A1; #define button 9 int color,number,number1,number2; unsigned long firstMillis1; unsigned long firstMillis2; unsigned long secondMillis1; Unsigned long variables are extended size variables for number storage and store 32 bits (4 bytes). // frequency is a double int32_t freq = frequency * 4294967296 / 180.0e6; That calculation is going to be done using floating point arithmetic. As @erenfro correctly noted, this isn't a bit width issue, as both int and long are 32 bit on Xtensa. I want to reinterpret the 32 bits of an unsigned long as a signed long. I don't think simply casting it to long will do the trick. In the Arduino int type (which is signed), if the high bit is a "1", the number is interpreted as a negative number, and the other 15 bits are interpreted with (2’s complement math). "double" is also a different size on ARM vs AVR. (Less plausibly, it could be unsigned char or unsigned short on an unusual system, or it could be an extended integer type; it cannot be unsigned long long, which is at least 64 bits wide.) and NEVER use the Arduino type “word” as that is defined to be “unsigned short” which is 16 bits on AVR and 32 bits on ARM and pic32. Example Unsigned Long velocity = 101006 ;// declaration of variable with type Unsigned Long and initialize it with 101006 It could plausibly be either unsigned int or unsigned long int. I would discourage using the “cutsie” Arduino types like byte. The difference between unsigned ints and (signed) ints, lies in the way the highest bit, sometimes referred to as the "sign" bit, is interpreted. So the only way to allow libraries to be portable between ESP32 Arduino core and other cores is to use unsigned long for the return value. The “word” type is a total fail. char vs signed char vs unsigned char. The library uses: uint8_t and uint16_t Until now I am only used of using the int and unsigned int (data types as described in the arduino … Which means that your fancy magic number on the right hand side is going to be truncated to about 6 decimal digits of precision anyway. It's 64bits on ARM, and only 32 (the same as "float") on AVR. You are likely wondering what are uint8_t, uint16_t, uint32_t and uint64_t. It turns out that they are equal respectively to: unsigned char, unsigned short, unsigned int and unsigned long long. But the size of uint32_t is always 32 bits independent of convention the compiler is following.. However in C++ int and long are different types, even if they are of the same size. You may use long type also for inet_addr() function since most of the architecture use 32 bits(4 bytes) for long type but it is not always applicable . But what are ranges of all these types? 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