Floating point cost on embedded systems in Embedded C - Mini Project: Build & Apply

Floating Point Cost on Embedded Systems

📖 Scenario: You are working on a small embedded system that controls a simple device. The system has limited memory and processing power. You want to understand how using floating point numbers affects the program's performance and size.

🎯 Goal: You will create a small program that calculates the sum of numbers using both integer and floating point types. This will help you see the difference in how floating point operations are handled on embedded systems.

📋 What You'll Learn

Create variables with exact names and values as instructed

Use integer and floating point types explicitly

Write simple loops to sum numbers

Print the results using printf

💡 Why This Matters

🌍 Real World

Embedded systems often have limited resources. Understanding floating point cost helps optimize performance and memory usage.

💼 Career

Embedded developers must write efficient code. Knowing when and how to use floating point types is important for system reliability and speed.

1

Create integer variables and initialize

Create an integer variable called int_sum and set it to 0. Create an integer variable called limit and set it to 100.

Embedded C

# Create integer variables int_sum and limit
// Your code here

Hint

Use int to declare integer variables and assign values with =.

2

Create floating point variables

Add a floating point variable called float_sum and set it to 0.0f. Add a floating point variable called float_limit and set it to 100.0f.

Embedded C

int int_sum = 0;
int limit = 100;
// Create float variables float_sum and float_limit
// Your code here

Hint

Use float type and add f after decimal numbers.

3

Sum numbers using loops

Write a for loop using int i from 1 to limit (inclusive) to add i to int_sum. Write another for loop using float j from 1.0f to float_limit (inclusive) adding j to float_sum with increments of 1.0f.

Embedded C

int int_sum = 0;
int limit = 100;
float float_sum = 0.0f;
float float_limit = 100.0f;
// Add for loops to sum integers and floats
// Your code here

Hint

Use two separate for loops with correct variable types and increments.

4

Print the results

Use printf to print the integer sum with the text "Integer sum: %d\n" and the floating point sum with the text "Floating point sum: %.1f\n".

Embedded C

int int_sum = 0;
int limit = 100;
float float_sum = 0.0f;
float float_limit = 100.0f;

for (int i = 1; i <= limit; i++) {
    int_sum += i;
}

for (float j = 1.0f; j <= float_limit; j += 1.0f) {
    float_sum += j;
}

// Print the sums
// Your code here

Hint

Use printf with %d for integers and %.1f for floats.

Practice

1. Why are floating point operations generally avoided on embedded systems?

easy

A. They require less memory than integer operations.

B. They consume more time and power compared to integer operations.

C. They always produce inaccurate results.

D. They are easier to implement than integer operations.

Solution

1. Step 1: Understand floating point vs integer operations

   Floating point operations involve more complex calculations than integer operations.

2. Step 2: Consider embedded system constraints

   Embedded systems have limited processing power and battery life, so slower and power-hungry operations are costly.

3. Final Answer:

   They consume more time and power compared to integer operations. -> Option B

4. Quick Check:

   Floating point cost = More time and power [OK]

Hint: Floating point = slower and power hungry on embedded [OK]

Common Mistakes:

• Thinking floating point uses less memory
• Assuming floating point is always more accurate
• Believing floating point operations are faster

2. Which of the following is the correct way to declare a floating point variable in embedded C?

easy

A. float temperature = 23.5;

B. int temperature = 23.5;

C. double temperature = '23.5';

D. float temperature = '23,5';

Solution

1. Step 1: Check variable type and value format

   Floating point variables use the keyword 'float' and values use dot (.) as decimal separator.

2. Step 2: Validate syntax correctness

   float temperature = 23.5; uses float and a correct decimal number with dot, so it is correct.

3. Final Answer:

   float temperature = 23.5; -> Option A

4. Quick Check:

   float with dot decimal = correct syntax [OK]

Hint: Use float keyword and dot decimal for floats [OK]

Common Mistakes:

• Using int for decimal numbers
• Using quotes around numbers
• Using comma instead of dot for decimals

3. What is the main drawback of this embedded C code snippet?

float a = 1.5f;
float b = 2.5f;
float c = a * b;
printf("%f", c);

medium

A. It uses floating point multiplication which is slower on embedded systems.

B. It will print an integer instead of a float.

C. It will cause a syntax error due to missing semicolons.

D. It uses incorrect format specifier in printf.

Solution

1. Step 1: Analyze the code operations

   The code multiplies two float variables and prints the result using %f, which is correct syntax.

2. Step 2: Consider embedded system performance

   Floating point multiplication is slower and consumes more power on embedded systems compared to integer operations.

3. Final Answer:

   It uses floating point multiplication which is slower on embedded systems. -> Option A

4. Quick Check:

   Floating point multiply = slower on embedded [OK]

Hint: Floating point math is slower than integer math [OK]

Common Mistakes:

• Thinking code has syntax errors
• Confusing format specifiers
• Assuming output is integer

4. Identify the error in this embedded C code snippet:

float x = 3.0;
int y = 2;
float z = x / y;
printf("%d", z);

medium

A. Variable z should be declared as int.

B. Division between float and int is not allowed.

C. Using %d to print a float variable causes incorrect output.

D. Missing semicolon after variable declarations.

Solution

1. Step 1: Check variable types and operations

   Variable z is float, result of float divided by int, which is valid and results in float.

2. Step 2: Check printf format specifier

   Using %d expects an int, but z is float, so output will be incorrect or undefined.

3. Final Answer:

   Using %d to print a float variable causes incorrect output. -> Option C

4. Quick Check:

   Printf %d with float = wrong output [OK]

Hint: Match printf format to variable type [OK]

Common Mistakes:

• Thinking division of float and int is invalid
• Assuming variable type declaration is wrong
• Ignoring printf format specifier importance

5. You want to optimize an embedded system program that calculates average sensor readings. Which approach best reduces floating point cost while keeping accuracy?

hard

A. Replace all floats with doubles for better precision.

B. Convert sensor readings to strings and parse them later.

C. Use floating point operations directly for all calculations.

D. Use integer arithmetic by scaling sensor values and divide after summing.

Solution

1. Step 1: Understand floating point cost and accuracy needs

   Floating point operations are costly; using integers scaled by a factor preserves accuracy and reduces cost.

2. Step 2: Evaluate options for optimization

   Use integer arithmetic by scaling sensor values and divide after summing. uses integer math with scaling, which is efficient and accurate. Replace all floats with doubles for better precision. increases cost. Use floating point operations directly for all calculations. ignores cost. Convert sensor readings to strings and parse them later. is inefficient and unnecessary.

3. Final Answer:

   Use integer arithmetic by scaling sensor values and divide after summing. -> Option D

4. Quick Check:

   Scale integers to avoid floats = efficient and accurate [OK]

Hint: Scale integers to avoid floats for efficiency [OK]

Common Mistakes:

• Assuming doubles are always better
• Ignoring floating point cost
• Using string conversions unnecessarily