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//===-- RegisterContext_x86.cpp ---------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "RegisterContext_x86.h"
using namespace lldb_private;
// Convert the 8-bit abridged FPU Tag Word (as found in FXSAVE) to the full
// 16-bit FPU Tag Word (as found in FSAVE, and used by gdb protocol). This
// requires knowing the values of the ST(i) registers and the FPU Status Word.
uint16_t lldb_private::AbridgedToFullTagWord(uint8_t abridged_tw, uint16_t sw,
llvm::ArrayRef<MMSReg> st_regs) {
// Tag word is using internal FPU register numbering rather than ST(i).
// Mapping to ST(i): i = FPU regno - TOP (Status Word, bits 11:13).
// Here we start with FPU reg 7 and go down.
int st = 7 - ((sw >> 11) & 7);
uint16_t tw = 0;
for (uint8_t mask = 0x80; mask != 0; mask >>= 1) {
tw <<= 2;
if (abridged_tw & mask) {
// The register is non-empty, so we need to check the value of ST(i).
uint16_t exp =
st_regs[st].comp.sign_exp & 0x7fff; // Discard the sign bit.
if (exp == 0) {
if (st_regs[st].comp.mantissa == 0)
tw |= 1; // Zero
else
tw |= 2; // Denormal
} else if (exp == 0x7fff)
tw |= 2; // Infinity or NaN
// 0 if normal number
} else
tw |= 3; // Empty register
// Rotate ST down.
st = (st - 1) & 7;
}
return tw;
}
// Convert the 16-bit FPU Tag Word to the abridged 8-bit value, to be written
// into FXSAVE.
uint8_t lldb_private::FullToAbridgedTagWord(uint16_t tw) {
uint8_t abridged_tw = 0;
for (uint16_t mask = 0xc000; mask != 0; mask >>= 2) {
abridged_tw <<= 1;
// full TW uses 11 for empty registers, aTW uses 0
if ((tw & mask) != mask)
abridged_tw |= 1;
}
return abridged_tw;
}
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