ProtobufDecimal.cs

public static Messages.Decimal BuildDecimal(decimal d)
{
  int[] bits = decimal.GetBits(d.Value);

  if (bits[2] != 0 || bits[1] < 0) throw new Exception("Unrepresentable decimal number. Out of range.");

  long value = (((long)bits[1]) << 32) | ((long)bits[0] & 0xFFFFFFFFL);
  if ((bits[3] & 0x80000000) != 0) value = -value;

  uint scale = ((uint)bits[3] >> 16) & 0xF;

  var builder = Messages.Decimal.CreateBuilder();
  builder.SetValue(value);
  if (scale != 0) builder.SetScale(scale);
  return builder.Build();
}

public static decimal ParseDecimal(Messages.Decimal d)
{
  if (!d.HasValue) throw new Exception("Expected value.");

  uint scale = d.Scale;
  if (scale > 28) throw new Exception("Invalid scale.");

  long value = d.Value;
  if (value < 0) value = -value;
  int[] bits = new int[] {
    (int)(value & 0xFFFFFFFFL),
    (int)((value >> 32) & 0xFFFFFFFFL),
    0,
    (((int)scale & 0x1F) << 16) | ((int)((d.Value >> 32) & 0x80000000))
  };
  return new decimal(bits);
}

ProtobufDecimal.java

public static Proto.Decimal buildDecimal(BigDecimal d)
{
  if (d == null) return null;
  
  BigInteger value = d.unscaledValue();
  
  if (value.compareTo(MAX_INT) > 0 || value.compareTo(MIN_INT) < 0)
    throw new RuntimeException("Unrepresentable decimal number. Out of range.");
  
  Proto.Decimal.Builder builder = Proto.Decimal.newBuilder();
  builder.setValue(value.longValue());
  if (d.scale() != 0) builder.setScale(d.scale());
  return builder.build();
}


public static BigDecimal parseDecimal(Proto.Decimal d)
{
  if (!d.hasValue()) throw new RuntimeException("Expected a scale.");
  return BigDecimal.valueOf(d.getValue(), d.hasScale() ? d.getScale() : 0);
}