examples/add2-vectors.cc

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#include "examples.h"

// Macro to compute the number of elements in a vector.
#define ARRAY_SIZE(Array) (sizeof(Array) / sizeof((Array)[0]))
#define BUF_SIZE (4096)
#define __ masm->

/*
 * This example adds two vectors with 1-byte elements using NEON instructions,
 * and returns the results in the first vector.
 */
void GenerateAdd2Vectors(MacroAssembler* masm) {
  // void add2_vectors(uint8_t *vec*, const uint8_t *vecB, unsigned size)
  // Argument locations:
  //    vecA (pointer) -> x0
  //    vecB (pointer) -> x1
  //    size (integer) -> w2
  // Result returned in vecA.

  Label loop16, loopr, end;

  // Loop to add vector elements in 16-byte chunks.
  __ Bind(&loop16);

  // Handle vectors smaller than 16-bytes in the remainder loop.
  __ Cmp(w2, 16);
  __ B(lo, &loopr);
  __ Sub(w2, w2, 16);

  // Add vectors in 16-byte chunks.
  __ Ld1(v0.V16B(), MemOperand(x0));
  __ Ld1(v1.V16B(), MemOperand(x1, 16, PostIndex));
  __ Add(v0.V16B(), v0.V16B(), v1.V16B());
  __ St1(v0.V16B(), MemOperand(x0, 16, PostIndex));

  __ B(&loop16);

  // Loop to add the remaining vector elements.
  __ Bind(&loopr);

  // If there are no more vector elements to process, then exit.
  __ Cbz(w2, &end);
  __ Sub(w2, w2, 1);

  // Add remaining vector elements in 1-byte chunks.
  __ Ldrb(w5, MemOperand(x0));
  __ Ldrb(w6, MemOperand(x1, 1, PostIndex));
  __ Add(w5, w5, w6);
  __ Strb(w5, MemOperand(x0, 1, PostIndex));

  __ B(&loopr);

  __ Bind(&end);

  __ Ret();
}


void PrintVector(const uint8_t* vec, unsigned num) {
  unsigned i;
  printf("( ");
  if (num > 0) {
    for (i = 0; i < num - 1; ++i) {
      printf("%d, ", vec[i]);
    }
    printf("%d", vec[i]);
  }
  printf(" )\n");
}


#ifndef TEST_EXAMPLES
int main(void) {
  // Create and initialize the assembler.
  byte assm_buf[BUF_SIZE];
  MacroAssembler masm(assm_buf, BUF_SIZE);

  // Generate native code for the example function.
  Label add2_vectors;
  masm.Bind(&add2_vectors);
  GenerateAdd2Vectors(&masm);
  masm.FinalizeCode();

  // Initialize input data for the example function.
  // clang-format: off
  uint8_t vecA[] = {0,  1,  2,  3,  4,  5,  6,  7,  8,  9,  10, 11, 12,
                    13, 14, 15, 0,  1,  2,  3,  4,  5,  6,  7,  8,  9,
                    10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20};
  uint8_t vecB[] = {16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28,
                    29, 30, 31, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,
                    26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36};
  // clang-format on
  uint8_t vecC[ARRAY_SIZE(vecA)];

  // Check whether the number of elements in both vectors match.
  assert(ARRAY_SIZE(vecA) == ARRAY_SIZE(vecB));

  // Compute the result in C.
  for (unsigned i = 0; i < ARRAY_SIZE(vecA); i++) {
    vecC[i] = vecA[i] + vecB[i];
  }

#ifdef VIXL_INCLUDE_SIMULATOR
  uintptr_t vecA_addr = reinterpret_cast<uintptr_t>(vecA);
  uintptr_t vecB_addr = reinterpret_cast<uintptr_t>(vecB);

  // Configure register environment in the simulator.
  Decoder decoder;
  Simulator simulator(&decoder);
  simulator.set_xreg(0, vecA_addr);
  simulator.set_xreg(1, vecB_addr);
  simulator.set_xreg(2, ARRAY_SIZE(vecA));
  PrintVector(vecA, ARRAY_SIZE(vecA));
  printf(" +\n");
  PrintVector(vecB, ARRAY_SIZE(vecB));

  // Run the example function in the simulator.
  simulator.RunFrom(masm.GetLabelAddress<Instruction*>(&add2_vectors));
  printf(" =\n");
  PrintVector(vecA, ARRAY_SIZE(vecA));
#else
  // Placeholder to run test natively.
  printf("Running tests natively is not supported yet.\n");
  return 0;
#endif  // VIXL_INCLUDE_SIMULATOR
  // Check that the computed value in NEON matches the C version.
  for (unsigned i = 0; i < ARRAY_SIZE(vecA); i++) {
    assert(vecC[i] == vecA[i]);
  }

  return 0;
}
#endif  // TEST_EXAMPLES