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26
27#include "examples.h"
28
29#define __ masm->
30
31void GenerateApproximatePi(MacroAssembler* masm) {
32  // double ApproximatePi(uint32_t iterations)
33  // Very rough approximation of pi
34  // pi/4 = 1 - 1/3 + 1/5 - 1/7 + ... + (-1)^n / (2n + 1)
35  __ Cmp(r0, 0);
36  __ Bx(eq, lr);
37  __ Vpush(Untyped64, DRegisterList(d8, 8));
38  __ Vldr(d0, 1.0);
39  __ Vldr(d1, 3.0);
40  __ Vldr(d2, 5.0);
41  __ Vldr(d3, 7.0);
42
43
44  __ Vmov(d4, 8.0);
45  __ Vmov(d5, 1.0);
46
47  __ Vmov(I64, d10, 0);  // d10 = 0.0;
48  __ Vmov(I64, d11, 0);  // d11 = 0.0;
49  __ Vmov(I64, d12, 0);  // d12 = 0.0;
50  __ Vmov(I64, d13, 0);  // d13 = 0.0
51
52  Label loop;
53  __ Bind(&loop);
54
55  __ Vdiv(F64, d6, d5, d0);
56  __ Vdiv(F64, d7, d5, d1);
57  __ Vdiv(F64, d8, d5, d2);
58  __ Vdiv(F64, d9, d5, d3);
59
60  __ Vadd(F64, d10, d10, d6);
61  __ Vadd(F64, d11, d11, d7);
62  __ Vadd(F64, d12, d12, d8);
63  __ Vadd(F64, d13, d13, d9);
64
65  __ Vadd(F64, d0, d0, d4);
66  __ Vadd(F64, d1, d1, d4);
67  __ Vadd(F64, d2, d2, d4);
68  __ Vadd(F64, d3, d3, d4);
69
70  __ Subs(r0, r0, 1);
71  __ B(ne, &loop);
72
73  __ Vmov(F64, d4, 4.0);
74  __ Vadd(F64, d10, d10, d12);
75  __ Vadd(F64, d11, d11, d13);
76  __ Vsub(F64, d10, d10, d11);
77  __ Vmul(F64, d0, d10, d4);
78  __ Vpop(Untyped64, DRegisterList(d8, 8));
79  __ Bx(lr);
80}
81
82#ifndef TEST_EXAMPLES
83int main() {
84  MacroAssembler masm;
85  // Generate the code for the example function.
86  Label pi_approx;
87  masm.Bind(&pi_approx);
88  GenerateApproximatePi(&masm);
89  masm.FinalizeCode();
90#ifdef VIXL_INCLUDE_SIMULATOR_AARCH32
91  // There is no simulator defined for VIXL AArch32.
92  printf("This example cannot be simulated\n");
93#else
94  byte* code = masm.GetBuffer()->GetStartAddress<byte*>();
95  uint32_t code_size = masm.GetSizeOfCodeGenerated();
96  ExecutableMemory memory(code, code_size);
97  // Run the example function.
98  double (*pi_function)(uint32_t) =
99      memory.GetEntryPoint<double (*)(uint32_t)>(pi_approx);
100  uint32_t repeat = 10000000;
101  double output_value = (*pi_function)(repeat);
102  printf("native: pi_approx(%u) = %3.10f\n", repeat, output_value);
103#endif
104  return 0;
105}
106#endif  // TEST_EXAMPLES
107