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Compare Time Libraries

This program compares the runtime performance of LocalDateTime::forEpochSeconds and the LocalDateTime::toEpochSeconds() methods in the AceTime library versus the equivalent breakTime() and makeTime() functions in the Arduino Time Library.

From the benchmarks below on various processors, I conclude that the LocalDateTime methods are;

  • 2-5X faster on an 8-bit AVR processor
  • 3-5X faster on an ESP8266
  • 7-8X faster on an ESP32
  • 7-8X faster on Teensy 3.2 controller

The main culprit for the slow speed of the makeTime() and breakTime() methods in the Arduino Time library is that they use a loop to count the number of days and seconds between the given date/time and the Unix epoch (1970-01-01). For dates around the current date/time (year 2018), these methods must add up 47 years worth of days, then loop over the remaining months, days and seconds in the current year. As the years pass, the number of cycles in those methods will increase and the performance will become worse.

In contrast, the AceTime library uses arithmetic formulas to convert between date/time components and epochSeconds. These expressions take the same amount of time regardless of the value of the year. They contain a fair number of integer division operations which are notoriously slow on 8-bit AVR processors because divisions are emulated in software instead of implemented in hardware. Even with the slow integer division operations, the AceTime library is faster on the AVR boards than the Arduino Time Library. On processors that support hardware divisions, the AceTime library can become an order of magnitude (10X) faster than the Arduino Time Library.

Arduino Nano

+----------------------------------+---------+
| Method                           |  micros |
|----------------------------------|---------|
| Empty loop                       |   4.500 |
|----------------------------------|---------|
| LocalDateTime::forEpochSeconds() | 271.000 |
| breakTime()                      | 595.500 |
|----------------------------------|---------|
| LocalDateTime::toEpochSeconds()  |  66.500 |
| makeTime()                       | 336.000 |
+----------------------------------+---------+
Number of iterations per run: 2000
Delta seconds: 236682

ESP8266

+----------------------------------+---------+
| Method                           |  micros |
|----------------------------------|---------|
| Empty loop                       |   0.900 |
|----------------------------------|---------|
| LocalDateTime::forEpochSeconds() |  15.200 |
| breakTime()                      |  45.600 |
|----------------------------------|---------|
| LocalDateTime::toEpochSeconds()  |   4.500 |
| makeTime()                       |  22.600 |
+----------------------------------+---------+
Number of iterations per run: 10000
Delta seconds: 47336

ESP32

+----------------------------------+---------+
| Method                           |  micros |
|----------------------------------|---------|
| Empty loop                       |   0.280 |
|----------------------------------|---------|
| LocalDateTime::forEpochSeconds() |   0.620 |
| breakTime()                      |   5.070 |
|----------------------------------|---------|
| LocalDateTime::toEpochSeconds()  |   0.560 |
| makeTime()                       |   4.310 |
+----------------------------------+---------+
Number of iterations per run: 100000
Delta seconds: 2366

Teensy 3.2

  • CPU Speed: 96 MHz
  • Compiler Optimization: "Faster"
+----------------------------------+---------+
| Method                           |  micros |
|----------------------------------|---------|
| Empty loop                       |   0.510 |
|----------------------------------|---------|
| LocalDateTime::forEpochSeconds() |   1.580 |
| breakTime()                      |  12.610 |
|----------------------------------|---------|
| LocalDateTime::toEpochSeconds()  |   1.170 |
| makeTime()                       |   9.780 |
+----------------------------------+---------+
Number of iterations per run: 100000
Delta seconds: 4733