Usage of fixed in c language

The usage of C language fixed refers to a technology that uses fixed point numbers to represent floating point numbers. In many embedded systems, due to limited hardware resources, floating point operations cannot be supported, but some complex calculations are required. , then you can use fixed instead of floating point numbers for calculations. fixed is a fixed-point number representation method that represents floating-point numbers as an integer and a fixed number of decimal places. Normally, fixed numbers have a fixed number of decimal places.

The fixed usage in C language refers to a technology that uses fixed point numbers to represent floating point numbers. In many embedded systems, due to limited hardware resources, floating point operations cannot be supported, but some complex calculations need to be performed. At this time, fixed can be used instead of floating point calculations.

fixed is a fixed-point number representation method that represents floating-point numbers as an integer and a fixed number of decimal places. Usually, the number of decimal places of a fixed value is fixed, such as 16-bit integer and 16-bit decimal, expressed in Q16.16 format. In this way, we can use integer operations instead of floating point operations, thereby improving computational efficiency.

In C language, we can use integer types to represent fixed values. Generally speaking, we can use the int type to represent fixed values, but in order to facilitate calculation and avoid overflow, we can define a new type to represent fixed values, such as using the typedef keyword to define a new type named fixed_t.

The following is a sample code that shows how to define and use fixed values:

#include <stdio.h>
typedef int fixed_t;
#define FIXED_BITS 16
#define FIXED_SCALE (1 << FIXED_BITS)
fixed_t float_to_fixed(float f) {
    return (fixed_t)(f * FIXED_SCALE);
}
float fixed_to_float(fixed_t fixed) {
    return (float)fixed / FIXED_SCALE;
}
fixed_t fixed_add(fixed_t a, fixed_t b) {
    return a + b;
}
fixed_t fixed_sub(fixed_t a, fixed_t b) {
    return a - b;
}
fixed_t fixed_mul(fixed_t a, fixed_t b) {
    return (fixed_t)(((int64_t)a * b) >> FIXED_BITS);
}
fixed_t fixed_div(fixed_t a, fixed_t b) {
    return (fixed_t)(((int64_t)a << FIXED_BITS) / b);
}
int main() {
    float a = 1.5;
    float b = 2.3;
    fixed_t fixed_a = float_to_fixed(a);
    fixed_t fixed_b = float_to_fixed(b);
    fixed_t fixed_sum = fixed_add(fixed_a, fixed_b);
    fixed_t fixed_diff = fixed_sub(fixed_a, fixed_b);
    fixed_t fixed_product = fixed_mul(fixed_a, fixed_b);
    fixed_t fixed_quotient = fixed_div(fixed_a, fixed_b);
    printf("a + b = %f\n", fixed_to_float(fixed_sum));
    printf("a - b = %f\n", fixed_to_float(fixed_diff));
    printf("a * b = %f\n", fixed_to_float(fixed_product));
    printf("a / b = %f\n", fixed_to_float(fixed_quotient));
    return 0;
}

In the above sample code, we define a fixed_t type to represent fixed values. First, we use the float_to_fixed function to convert a floating point number to a fixed value, and then use the fixed_to_float function to convert a fixed value to a floating point number.

Next, we implemented some basic fixed arithmetic functions, including addition, subtraction, multiplication and division. These functions use integer arithmetic instead of floating point arithmetic, making calculations more efficient.

Finally, in the main function, we demonstrate how to use fixed values ​​to perform calculations and print the results.

It should be noted that when using fixed values ​​for calculation, you need to pay attention to the problem of overflow. Since the number of decimal places in fixed values ​​is fixed, when multiplication and division operations are performed, the result may overflow. Therefore, when performing multiplication and division operations, we need to use 64-bit integers to save intermediate results and perform appropriate bit shift operations to avoid overflow.

In summary, fixed usage in C language is a technology that represents floating point numbers as fixed point numbers, which can improve calculation efficiency. By defining new types and implementing corresponding arithmetic functions, we can easily use fixed values ​​for calculations. However, you need to pay attention to the problem of overflow, choose the number of integers and decimal places reasonably, and perform appropriate displacement operations to ensure the correctness of the calculation.

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