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135 lines
2.7 KiB
135 lines
2.7 KiB
#if defined(R3000)
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/*++
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Copyright (c) 1992 Microsoft Corporation
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Module Name:
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softsqrt.c
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Abstract:
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This module implements single precision IEEE square root.
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Author:
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David N. Cutler (davec) 16-Nov-1992
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Environment:
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User mode only.
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Revision History:
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--*/
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#include "nt.h"
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#include "ntrtl.h"
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#include "nturtl.h"
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#include "windows.h"
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//
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// Define square root table.
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//
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ULONG GreSquareRootTable[] = {
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83599, 71378, 60428, 50647, 41945, 34246, 27478, 21581,
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16499, 12183, 8588, 5674, 3403, 1742, 661, 130,
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0, 1204, 3062, 5746, 9193, 13348, 18162, 23592,
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29598, 36145, 43202, 50740, 58733, 67158, 75992, 85215};
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VOID
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vSqrtEFLOAT (
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IN PFLOAT Value
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)
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/*++
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Routine Description:
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This function computes the single precision IEEE square root of a
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specified value.
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N.B. The algorithm used is taken from the MIPS math library. It
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produces results that are 100% IEEE compliant and compatible
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with the R4000 square root instruction.
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Arguments:
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Value - Supplies a pointer to the value for which the square root is
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computed.
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Return Value:
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The single precision square root of the specified value is returned as
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the function value.
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--*/
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{
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DOUBLE DoubleValue;
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ULONG Index;
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FLOAT SingleEstimate;
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FLOAT SingleResult;
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FLOAT SingleValue;
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DOUBLE TempValue;
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union {
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DOUBLE DoubleEstimate;
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struct {
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ULONG LowPart;
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ULONG HighPart;
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} s;
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} u;
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//
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// Extract bits 19-23 of the mantissa to select the correct entry from
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// the square root table.
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//
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SingleValue = *Value;
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Index = ((*(PULONG)&SingleValue) >> 19) & 0x1f;
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//
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// Bias the mantissa by (127 << 23) - (127 << 22) and subtract out the
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// value selected from the square root table multipled by eight.
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//
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*((PULONG)&SingleEstimate) = (((*(PULONG)&SingleValue) >> 1) +
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((127 << 23) - (127 << 22))) - (GreSquareRootTable[Index] << 3);
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//
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// Refine the estimate value.
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//
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SingleEstimate = SingleEstimate + *Value / SingleEstimate;
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*((PULONG)&SingleEstimate) = *(PULONG)&SingleEstimate - ((1 << 23) + (6 << 3));
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//
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// Convert to double precision.
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//
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u.DoubleEstimate = SingleEstimate;
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DoubleValue = *Value;
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//
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// Refine the estimate value.
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//
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u.DoubleEstimate = u.DoubleEstimate + DoubleValue / u.DoubleEstimate;
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TempValue = DoubleValue / u.DoubleEstimate;
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u.s.HighPart -= (2 << 20);
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//
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// Compute the final result and convert to single precision.
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//
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SingleResult = u.DoubleEstimate + TempValue;
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*Value = SingleResult;
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return;
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}
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#endif
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