---
name: "fixsub"
section: "3alleg4"
platform: "linux"
package: "allegro4-doc"
version: "2:4.4.3.1-5"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/fixsub/3alleg4"
---

# fixsub(3alleg4)

Safe function to subtract fixed point numbers clamping underflow. Allegro game programming library.

## NAME

fixsub - Safe function to subtract fixed point numbers clamping underflow. Allegro game programming library.

## SYNOPSIS

**#include \<allegro.h\>**

**fixed fixsub(fixed x, fixed y);**

## DESCRIPTION

Although fixed point numbers can be subtracted with the normal '-' integer operator, that doesn't provide any protection against overflow. If overflow is a problem, you should use this function instead. It is slower than using integer operators, but if an overflow occurs it will set \`errno' and clamp the result, rather than just letting it wrap. Example:

```
   fixed result;
   /* This will put 4965 into `result'. */
   result = fixsub(itofix(5000), itofix(35));
   /* Sets `errno' and puts -32768 into `result'. */
   result = fixsub(itofix(-31000), itofix(3000));
   ASSERT(!errno); /* This will fail. */
```

## RETURN VALUE

Returns the clamped result of subtracting \`y' from \`x', setting \`errno' to ERANGE if there was an overflow.

## SEE ALSO

**fixadd**(3alleg4), **fixmul**(3alleg4), **fixdiv**(3alleg4)