1al_fixed(3) Library Functions Manual al_fixed(3)
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6 al_fixed
7
9 #include <allegro5/allegro.h>
10 typedef int32_t al_fixed;
12
14 A fixed point number.
15 Allegro provides some routines for working with fixed point numbers,
17 and defines the type al_fixed to be a signed 32-bit integer. The high
18 word is used for the integer part and the low word for the fraction,
19 giving a range of –32768 to 32767 and an accuracy of about four or five
20 decimal places. Fixed point numbers can be assigned, compared, added,
21 subtracted, negated and shifted (for multiplying or dividing by powers
22 of two) using the normal integer operators, but you should take care to
23 use the appropriate conversion routines when mixing fixed point with
24 integer or floating point values. Writing
25 fixed_point_1 + fixed_point_2 is OK, but fixed_point + integer is not.
26 The only advantage of fixed point math routines is that you don't
28 require a floating point coprocessor to use them. This was great in
29 the time period of i386 and i486 machines, but stopped being so useful
30 with the coming of the Pentium class of processors. From Pentium
31 onwards, CPUs have increased their strength in floating point opera‐
32 tions, equaling or even surpassing integer math performance.
33 Depending on the type of operations your program may need, using float‐
35 ing point types may be faster than fixed types if you are targeting a
36 specific machine class. Many embedded processors have no FPUs so fixed
37 point maths can be useful there.
38Allegro reference manual al_fixed(3)