TASKING VX-toolset for ARM User Guide

TASKING VX-toolset for ARM User GuideEspecially for large switch statements, the jump table approach executes faster than the binary searchtable approach. Also the jump table has a predictable behavior in execution speed: independent of theswitch argument, every case is reached in the same execution time. However, when the case labels aredistributed far apart, the jump table becomes sparse, wasting code memory. The compiler will not usethe jump table method when the waste becomes excessive.With a small number of cases, the jump chain method can be faster in execution and shorter in size.For ARMv7M a switch using the tbh instruction gets priority over a normal switch table implementation.How to overrule the default switch methodYou can overrule the compiler chosen switch method by using a pragma:#pragma linear_switch#pragma jump_switch#pragma binary_switch#pragma smart_switch#pragma tbb_switch#pragma tbh_switch#pragma no_tbh_switchforce jump chain codeforce jump table codeforce binary search table codelet the compiler decide the switch method usedforce use of tbb instruction (uses a table of 8-bit jump offsets)force use of tbh instruction (uses a table of 16-bit jump offsets)same as smart_switch, but do not use tbh instructionUsing a pragma cannot overrule the restrictions as described earlier.The switch pragmas must be placed before the switch statement. Nested switch statements use thesame switch method, unless the nested switch is implemented in a separate function which is precededby a different switch pragma.Example:/* place pragma before function body */#pragma jump_switchvoid test(unsigned char val){ /* function containing the switch */switch (val){/* use jump table */}}22