Store character mappings in PROGMEM #8
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This allows sketches to successfully link when this library is included in multiple files.
Arduino Uno has only a feeble 2 kilobytes of RAM. As data are put into RAM by default on AVR, the conversion tables will easily eat up all the precious RAM space. Declaring the tables PGMSPACE should solve the RAM usage and make it compatible with AVR again.
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This patchset stores character mappings in PROGMEM, which explicitly instructs the compiler to not load them into RAM at program startup. In turn, these mappings require special macros from
<avr/pgmspace.h>to read. This reduces the RAM overhead of this library to a minimum. For portability,<avr/pgmspace.h>is indirectly included via the Arduino core's main header,<Arduino.h>, which provides the macros as no-ops on non-AVR platforms.To counteract the slower speed of loading from ROM (LPM takes 3 cycles on Uno, while LD takes 2), The character tables are sorted by code point in ascending order, and
bsearch()is used for lookup.