23 May
2015
23 May
'15
2:50 a.m.
Author: aandrejevic
Date: Sat May 23 02:50:11 2015
New Revision: 67855
URL: http://svn.reactos.org/svn/reactos?rev=67855&view=rev
Log:
[FAST486]
Use a better algorithm for the base 2 logarithm.
Put the shared code for FPREM and FPREM1 in an inline function used by both.
Modified:
trunk/reactos/lib/fast486/fpu.c
Modified: trunk/reactos/lib/fast486/fpu.c
URL:
http://svn.reactos.org/svn/reactos/trunk/reactos/lib/fast486/fpu.c?rev=6785…
==============================================================================
--- trunk/reactos/lib/fast486/fpu.c [iso-8859-1] (original)
+++ trunk/reactos/lib/fast486/fpu.c [iso-8859-1] Sat May 23 02:50:11 2015
@@ -52,6 +52,9 @@
/* ln(2) */
static const FAST486_FPU_DATA_REG FpuLnTwo = {0xB17217F7D1CF79ABULL, FPU_REAL10_BIAS - 1,
FALSE};
+
+/* 2.00 */
+static const FAST486_FPU_DATA_REG FpuTwo = {0x8000000000000000ULL, FPU_REAL10_BIAS + 1,
FALSE};
static const FAST486_FPU_DATA_REG FpuInverseNumber[INVERSE_NUMBERS_COUNT] =
{
@@ -1105,11 +1108,6 @@
*Result = TempResult;
}
-/*
- * Calculates using the identities:
- * log2(x) = ln(x) / ln(2)
- * ln(x)= sum { -1^(n+1) * x^n / n!, n >= 1 }
- */
static inline BOOLEAN FASTCALL
Fast486FpuCalculateLogBase2(PFAST486_STATE State,
PFAST486_FPU_DATA_REG Operand,
@@ -1117,7 +1115,6 @@
{
INT i;
FAST486_FPU_DATA_REG Value = *Operand;
- FAST486_FPU_DATA_REG SeriesElement;
FAST486_FPU_DATA_REG TempResult;
FAST486_FPU_DATA_REG TempValue;
LONGLONG UnbiasedExp = (LONGLONG)Operand->Exponent - FPU_REAL10_BIAS;
@@ -1163,40 +1160,31 @@
Value.Mantissa <<= Bits;
}
- /* Subtract one from the value */
- if (!Fast486FpuSubtract(State, &Value, &FpuOne, &Value)) return FALSE;
-
- /* Calculate the natural logarithm */
- SeriesElement = TempResult = Value;
-
- for (i = 2; i < INVERSE_NUMBERS_COUNT / 2; i++)
- {
- if (!Fast486FpuMultiply(State, &SeriesElement, &Value,
&SeriesElement))
- {
- /* An exception occurred */
- return FALSE;
- }
-
- /* Toggle the sign of the series element */
- SeriesElement.Sign = !SeriesElement.Sign;
-
- /* Divide it by the counter */
- if (!Fast486FpuMultiply(State, &SeriesElement, &FpuInverseNumber[i - 1],
&TempValue))
- {
- /* An exception occurred */
- return FALSE;
- }
-
- /* And add it to the result */
- if (!Fast486FpuAdd(State, &TempResult, &TempValue, &TempResult))
- {
- /* An exception occurred */
- return FALSE;
- }
- }
-
- /* Now convert the natural logarithm into a base 2 logarithm */
- if (!Fast486FpuDivide(State, &TempResult, &FpuLnTwo, &TempResult)) return
FALSE;
+ TempResult.Sign = FALSE;
+ TempResult.Exponent = FPU_REAL10_BIAS - 1;
+ TempResult.Mantissa = 0ULL;
+
+ for (i = 63; i >= 0; i--)
+ {
+ /* Square the value */
+ if (!Fast486FpuMultiply(State, &Value, &Value, &Value)) return
FALSE;
+
+ /* Subtract two from it */
+ if (!Fast486FpuSubtract(State, &Value, &FpuTwo, &TempValue)) return
FALSE;
+
+ /* Is the result positive? */
+ if (!TempValue.Sign)
+ {
+ /* Yes, set the appropriate bit in the mantissa */
+ TempResult.Mantissa |= 1ULL << i;
+
+ /* Halve the value */
+ if (!Fast486FpuMultiply(State, &Value, &FpuInverseNumber[1],
&Value)) return FALSE;
+ }
+ }
+
+ /* Normalize the result */
+ if (!Fast486FpuNormalize(State, &TempResult)) return FALSE;
/*
* Add the exponent to the result
@@ -1207,6 +1195,35 @@
*Result = TempResult;
return TRUE;
+}
+
+static inline BOOLEAN FASTCALL
+Fast486FpuRemainder(PFAST486_STATE State,
+ PCFAST486_FPU_DATA_REG FirstOperand,
+ PCFAST486_FPU_DATA_REG SecondOperand,
+ BOOLEAN RoundToNearest,
+ PFAST486_FPU_DATA_REG Result)
+{
+ BOOLEAN Success = FALSE;
+ INT OldRoundingMode = State->FpuControl.Rc;
+ LONGLONG Integer;
+ FAST486_FPU_DATA_REG Temp;
+
+ if (!Fast486FpuDivide(State, FirstOperand, SecondOperand, &Temp)) return FALSE;
+
+ State->FpuControl.Rc = RoundToNearest ? FPU_ROUND_NEAREST : FPU_ROUND_TRUNCATE;
+
+ if (!Fast486FpuToInteger(State, &Temp, &Integer)) goto Cleanup;
+ Fast486FpuFromInteger(State, Integer, &Temp);
+
+ if (!Fast486FpuMultiply(State, &Temp, SecondOperand, &Temp)) goto Cleanup;
+ if (!Fast486FpuSubtract(State, FirstOperand, &Temp, Result)) goto Cleanup;
+
+ Success = TRUE;
+
+Cleanup:
+ State->FpuControl.Rc = OldRoundingMode;
+ return Success;
}
/*
@@ -2008,10 +2025,6 @@
/* FPREM1 */
case 0x35:
{
- FAST486_FPU_DATA_REG Temp;
- LONGLONG Integer;
- INT OldRoundingMode = State->FpuControl.Rc;
-
if (FPU_GET_TAG(0) == FPU_TAG_EMPTY || FPU_GET_TAG(1) == FPU_TAG_EMPTY)
{
State->FpuStatus.Ie = TRUE;
@@ -2020,34 +2033,9 @@
break;
}
- /* Divide ST0 by ST1 */
- if (!Fast486FpuDivide(State, &FPU_ST(0), &FPU_ST(1), &Temp))
break;
-
- /* Round the result to the nearest integer */
- if (FPU_ST(0).Exponent < FPU_REAL10_BIAS + 63)
- {
- State->FpuControl.Rc = FPU_ROUND_NEAREST;
-
- if (Fast486FpuToInteger(State, &Temp, &Integer))
- {
- Fast486FpuFromInteger(State, Integer, &Temp);
- State->FpuControl.Rc = OldRoundingMode;
- }
- else
- {
- /* Restore the rounding mode and exit */
- State->FpuControl.Rc = OldRoundingMode;
- break;
- }
- }
-
- /* Multiply the result by ST1 */
- if (!Fast486FpuMultiply(State, &Temp, &FPU_ST(1), &Temp))
break;
-
- /* Subtract the result from ST0 */
- if (!Fast486FpuSubtract(State, &FPU_ST(0), &Temp,
&FPU_ST(0))) break;
-
+ Fast486FpuRemainder(State, &FPU_ST(0), &FPU_ST(1), TRUE,
&FPU_ST(0));
FPU_UPDATE_TAG(0);
+
break;
}
@@ -2068,10 +2056,6 @@
/* FPREM */
case 0x38:
{
- FAST486_FPU_DATA_REG Temp;
- LONGLONG Integer;
- INT OldRoundingMode = State->FpuControl.Rc;
-
if (FPU_GET_TAG(0) == FPU_TAG_EMPTY || FPU_GET_TAG(1) == FPU_TAG_EMPTY)
{
State->FpuStatus.Ie = TRUE;
@@ -2080,34 +2064,9 @@
break;
}
- /* Divide ST0 by ST1 */
- if (!Fast486FpuDivide(State, &FPU_ST(0), &FPU_ST(1), &Temp))
break;
-
- /* Round the result to an integer, towards zero */
- if (FPU_ST(0).Exponent < FPU_REAL10_BIAS + 63)
- {
- State->FpuControl.Rc = FPU_ROUND_TRUNCATE;
-
- if (Fast486FpuToInteger(State, &Temp, &Integer))
- {
- Fast486FpuFromInteger(State, Integer, &Temp);
- State->FpuControl.Rc = OldRoundingMode;
- }
- else
- {
- /* Restore the rounding mode and exit */
- State->FpuControl.Rc = OldRoundingMode;
- break;
- }
- }
-
- /* Multiply the result by ST1 */
- if (!Fast486FpuMultiply(State, &Temp, &FPU_ST(1), &Temp))
break;
-
- /* Subtract the result from ST0 */
- if (!Fast486FpuSubtract(State, &FPU_ST(0), &Temp,
&FPU_ST(0))) break;
-
+ Fast486FpuRemainder(State, &FPU_ST(0), &FPU_ST(1), FALSE,
&FPU_ST(0));
FPU_UPDATE_TAG(0);
+
break;
}