Category: Uncategorized

fp64lib was primarely targeted to be used as a library in the Arduino IDE. There it works successfully, on both Windows and Linux. However, some users tried to use it outside the Arduino IDE with some success, but also with some errors. As part of a debugging session, I created a small makefile that supports the usual targets “all” and “clean” and creates a library named libfp64.a, which you can then link and use in your projects.

When using fp64lib outside of the arduino IDE, segment allocation by the linker will be different. On some files, the propoer segment allocation was missing, resulting in error messages like

relocation truncated to fit: R_AVR_13_PCREL against `no symbol'

V1.1.9 now has proper segment allocation for all files.

In about 2/3 of all source files, common subroutines were identified and factored out. Overall flash footprint of the library could be reduced by about 350 Bytes, with some increase in execution times (about 5% on average). For example, memory footprint for Nerdcalc (see History) was 30642 Bytes with fp64lib V1.0.7. With V1.1.7, this was already down to 29596 – the savings of 1046 bytes came from the leaner trigonometric routines introduced in V1.1.0. And with V1.1.8 it is now at 29230 Bytes, so another 336 Bytes saved – and Nerdcalc does not use all fp64lib-functions.

The include file fp64lib.h was cleaned up and contains now only the official entry points of the library.

A bug was fixed in fp64_add to fix the incorrect result when adding 0 to a subnormal.

More details can be found on the fp64lib github release note.

Some functions did clobber the registers, thus nesting functions calls like fp64_mul(fp64_div(a,b),c) did not working correctly, when b or c where constants or variables.

Based on a proposal by @gjlayde on https://www.mikrocontroller.net/topic/85256#6137882, speed of fp64_sin could be improved by another 45%, using an optimized polynomial approximation for x in range [0,PI/2[.

Based on a proposal by @gjlayde on https://www.mikrocontroller.net/topic/85256#6133370, speed of fp64_log could be improved by another 40%. Instead of approximating log(x) in the range [1;2[, it is faster to approximate it in [1/sqrt(2); sqrt(2)] with same accuracy.

V1.1.3 is available for download, fixing a linker relocation error.

Fixed incorrect library.properties file.

V1.1.0 contained an linker symbol that was no longer available, V1.1.1 corrects that bug.

All basic functions were restructured to allow access to full internal 56-bit precision. This was necessary to completely rewrite all trigonometric functions and to update logarithm and exponential functions. As a result, most higher math functions (like sin, cos, tan, asin, acos, atan, log and exp) have now increased precision and reduced execution time, still with small code size. As an example, execution time for fp64_sin is now between 600 and 650 micro seconds on a standard, 16 MHz Arduino MEGA 2560 – or 9500 to 10500 ticks (instructions).

V1.1.0 also includes some minor bugfixes and code improvements.