examples/check-bounds.cc

// Copyright 2014, ARM Limited
// All rights reserved.
//
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#include "examples.h"

#define BUF_SIZE (4096)
#define __ masm->

void GenerateCheckBounds(MacroAssembler* masm) {
  // uint64_t check_bounds(uint64_t value, uint64_t low, uint64_t high)
  // Argument locations:
  //   value -> x0
  //   low   -> x1
  //   high  -> x2

  // First we compare 'value' with the 'low' bound. If x1 <= x0 the N flag will
  // be cleared. This configuration can be checked with the 'pl' condition.
  __ Cmp(x0, x1);

  // Now we will compare 'value' and 'high' (x0 and x2) but only if the 'pl'
  // condition is verified. If the condition is not verified, we will clear
  // all the flags except the carry one (C flag).
  __ Ccmp(x0, x2, CFlag, pl);

  // We set x0 to 1 only if the 'ls' condition is satisfied.
  // 'ls' performs the following test: !(C==1 && Z==0). If the previous
  // comparison has been skipped we have C==1 and Z==0, so the 'ls' test
  // will fail and x0 will be set to 0.
  // Otherwise if the previous comparison occurred, x0 will be set to 1
  // only if x0 is less than or equal to x2.
  __ Cset(x0, ls);

  __ Ret();
}


#ifndef TEST_EXAMPLES
#ifdef VIXL_INCLUDE_SIMULATOR
void run_function(Simulator* simulator,
                  Instruction* function,
                  uint64_t value,
                  uint64_t low,
                  uint64_t high) {
  simulator->set_xreg(0, value);
  simulator->set_xreg(1, low);
  simulator->set_xreg(2, high);

  simulator->RunFrom(function);
  printf("%" PRIu64 " %s between %" PRIu64 " and %" PRIu64 "\n",
         value,
         simulator->xreg(0) ? "is" : "is not",
         low,
         high);

  simulator->ResetState();
}

int main(void) {
  // Create and initialize the assembler and the simulator.
  byte assm_buf[BUF_SIZE];
  MacroAssembler masm(assm_buf, BUF_SIZE);
  Decoder decoder;
  Simulator simulator(&decoder);

  // Generate the code for the example function.
  Label check_bounds;
  masm.Bind(&check_bounds);
  GenerateCheckBounds(&masm);
  masm.FinalizeCode();

  // Run the example function.
  Instruction* function = masm.GetLabelAddress<Instruction*>(&check_bounds);
  run_function(&simulator, function, 546, 50, 1000);
  run_function(&simulator, function, 62, 100, 200);
  run_function(&simulator, function, 200, 100, 200);

  return 0;
}
#else
// Without the simulator there is nothing to test.
int main(void) { return 0; }
#endif  // VIXL_INCLUDE_SIMULATOR
#endif  // TEST_EXAMPLES