Created
January 31, 2018 16:57
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using System; | |
using System.Diagnostics; | |
using System.Runtime.CompilerServices; | |
using System.Threading; | |
namespace ConsoleApp3 | |
{ | |
class Program | |
{ | |
static void Main(string[] args) | |
{ | |
byte[] rand = GetRandom(); | |
char hi = default, lo = default; | |
var sw = new Stopwatch(); | |
while (true) | |
{ | |
sw.Restart(); | |
for (int j = 0; j < 500_000; j++) | |
{ | |
for (int i = 0; i < rand.Length; i++) | |
{ | |
BinaryToHex2(rand[i], out hi, out lo); | |
} | |
} | |
Console.WriteLine(sw.ElapsedMilliseconds); | |
GC.KeepAlive(hi); | |
GC.KeepAlive(lo); | |
} | |
} | |
[MethodImpl(MethodImplOptions.NoInlining)] | |
private static byte[] GetRandom() | |
{ | |
var rbg = new Random(0x1234); | |
byte[] retVal = new byte[1024]; | |
rbg.NextBytes(retVal); | |
return retVal; | |
} | |
// 'valueIfTrue' and 'valueIfFalse' really should be compile-time constants for maximum throughput. | |
[MethodImpl(MethodImplOptions.AggressiveInlining)] | |
private static int ConditionalSelect(bool condition, int valueIfTrue, int valueIfFalse) | |
{ | |
// From https://software.intel.com/sites/default/files/managed/9e/bc/64-ia-32-architectures-optimization-manual.pdf | |
// Example 3.2. We're taking advantage of the fact that bools are passed by value as 32-bit integers, | |
// so we'll blit it directly into a 1 or a 0 without a jump. | |
// Codegen will emit a movzx, but on Ivy Bridge (and later) the CPU itself elides the instruction. | |
return ((-Unsafe.As<bool, int>(ref condition)) & (valueIfTrue - valueIfFalse)) + valueIfFalse; | |
} | |
[MethodImpl(MethodImplOptions.AggressiveInlining)] | |
private static int ToInt(bool b) | |
{ | |
return Unsafe.As<bool, int>(ref b); | |
} | |
[MethodImpl(MethodImplOptions.AggressiveInlining)] | |
private static uint ToUInt(bool b) | |
{ | |
return Unsafe.As<bool, uint>(ref b); | |
} | |
[MethodImpl(MethodImplOptions.AggressiveInlining)] | |
private static void BinaryToHex1(byte b, out char hi, out char lo) | |
{ | |
hi = (char)((b >> 4) + ((b < (10 << 4)) ? '0' : ('A' - 10))); | |
b &= 0xF; | |
lo = (char)(b + ((b < 10) ? '0' : ('A' - 10))); | |
} | |
[MethodImpl(MethodImplOptions.AggressiveInlining)] | |
private static void BinaryToHex2(byte b, out char hi, out char lo) | |
{ | |
uint bVal = b; // MOVZX (elided) | |
bVal = (bVal >> 4) | (bVal << 28); // ROR | |
uint firstNibbleMultiplier = ToUInt((byte)bVal >= 10); // CMP and SETGE | |
hi = (char)((firstNibbleMultiplier * 8 + bVal + '0') - firstNibbleMultiplier); // LEA, SUB, MOVZX | |
bVal >>= 28; // SHR | |
uint secondNibbleMultiplier = ToUInt((byte)bVal >= 10); // CMP and SETGE | |
lo = (char)((secondNibbleMultiplier * 8 + bVal + '0') - secondNibbleMultiplier); // LEA, SUB, MOVZX | |
} | |
} | |
} |
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