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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
using System.Diagnostics;
using System.Runtime;
using System.Globalization;
namespace System
{
internal partial class Number
{
// buffer size to hold digits (40), decimal point, number sign, exponent, exponent symbol 'e', exponent sign and null.
private const int MAX_BUFFER_SIZE = 50;
private static unsafe void DoubleToNumber(double value, int precision, ref NumberBuffer number)
{
Debug.Assert(precision > 0 && precision < 40);
number.precision = precision;
if (!Double.IsFinite(value))
{
number.scale = Double.IsNaN(value) ? ScaleNAN : ScaleINF;
number.sign = Double.IsNegative(value);
number.digits[0] = '\0';
return;
}
byte* tempBuffer = stackalloc byte[MAX_BUFFER_SIZE];
char* dst = number.digits;
number.scale = 0;
number.sign = false;
*dst = '\0';
if (value < 0.0)
{
number.sign = true;
}
if (value == 0.0)
{
for (int j = 0; j < precision; j++)
{
dst[j] = '0';
}
dst[precision] = '\0';
return;
}
//
// Get the number formatted as a string in the form x.xxxxxxexxxx
//
// "%.40e"
byte* format = stackalloc byte[6];
format[0] = (byte)'%';
format[1] = (byte)'.';
format[2] = (byte)'4';
format[3] = (byte)'0';
format[4] = (byte)'e';
format[5] = 0;
int tempBufferLength = Interop.Sys.DoubleToString(value, format, tempBuffer, MAX_BUFFER_SIZE);
Debug.Assert(tempBufferLength > 0 && MAX_BUFFER_SIZE > tempBufferLength);
//
// Calculate the exponent value
//
int exponentIndex = tempBufferLength - 1;
while (tempBuffer[exponentIndex] != (byte)'e' && exponentIndex > 0)
{
exponentIndex--;
}
Debug.Assert(exponentIndex > 0 && (exponentIndex < tempBufferLength - 1));
int i = exponentIndex + 1;
int exponentSign = 1;
if (tempBuffer[i] == '-')
{
exponentSign = -1;
i++;
}
else if (tempBuffer[i] == '+')
{
i++;
}
int exponentValue = 0;
while (i < tempBufferLength)
{
Debug.Assert(tempBuffer[i] >= (byte)'0' && tempBuffer[i] <= (byte)'9');
exponentValue = exponentValue * 10 + (tempBuffer[i] - (byte)'0');
i++;
}
exponentValue *= exponentSign;
//
// Determine decimal location.
//
if (exponentValue == 0)
{
number.scale = 1;
}
else
{
number.scale = exponentValue + 1;
}
//
// Copy the string from the temp buffer upto precision characters, removing the sign, and decimal as required.
//
i = 0;
int mantissaIndex = 0;
while (i < precision && mantissaIndex < exponentIndex)
{
if (tempBuffer[mantissaIndex] >= (byte)'0' && tempBuffer[mantissaIndex] <= (byte)'9')
{
dst[i] = (char)tempBuffer[mantissaIndex];
i++;
}
mantissaIndex++;
}
while (i < precision)
{
dst[i] = '0'; // append zeros as needed
i++;
}
dst[i] = '\0';
//
// Round if needed
//
if (mantissaIndex >= exponentIndex || tempBuffer[mantissaIndex] < (byte)'5')
{
return; // rounding is not needed
}
i = precision - 1;
while (dst[i] == '9' && i > 0)
{
dst[i] = '0';
i--;
}
if (i == 0 && dst[i] == '9')
{
dst[i] = '1';
number.scale++;
}
else
{
dst[i]++;
}
}
}
}
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