CODEWITHSUNDEEP
c
user6053898
user6053898

Reputation: 11

Typecasting in C for each of the variables

What is the difference between the following two?

// uint8_t a; uint8_t b;

uint16_t first = (uint16_t)(a * b);

uint16_t second = (uint16_t)a * (uint16_t)b;

What could be the use cases of these two kinds of implementations?

Upvotes: 1

Views: 47

Answers (1)

chux
chux

Reputation: 154166

The mathematical product of a*b is in the range [0...65,025].

If unsigned/int is 32-bit, no difference.

If unsigned/int is 16-bit, a * b risks signed int overflow and undefined behavior (UB). Both a, b are converted to int prior to the multiplication and a*b may exceed INT_MAX (32,767).

(uint16_t)a * (uint16_t)b; is better.

Upvotes: 2

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