Move some conversion functions (IEEE double <-> x87 extended-real
format) into their own module, so they can be shared by the x86 and
amd64 front ends.
git-svn-id: svn://svn.valgrind.org/vex/trunk@1097 8f6e269a-dfd6-0310-a8e1-e2731360e62c
diff --git a/priv/guest-generic/g_generic_x87.c b/priv/guest-generic/g_generic_x87.c
new file mode 100644
index 0000000..7c9aa6d
--- /dev/null
+++ b/priv/guest-generic/g_generic_x87.c
@@ -0,0 +1,431 @@
+
+/*---------------------------------------------------------------*/
+/*--- ---*/
+/*--- This file (guest-generic/g_generic_x87.c) is ---*/
+/*--- Copyright (c) 2005 OpenWorks LLP. All rights reserved. ---*/
+/*--- ---*/
+/*---------------------------------------------------------------*/
+
+/*
+ This file is part of LibVEX, a library for dynamic binary
+ instrumentation and translation.
+
+ Copyright (C) 2004-2005 OpenWorks, LLP.
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; Version 2 dated June 1991 of the
+ license.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE, or liability
+ for damages. See the GNU General Public License for more details.
+
+ Neither the names of the U.S. Department of Energy nor the
+ University of California nor the names of its contributors may be
+ used to endorse or promote products derived from this software
+ without prior written permission.
+
+ You should have received a copy of the GNU General Public License
+ along with this program; if not, write to the Free Software
+ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
+ USA.
+*/
+
+/* This file contains functions for doing some x87-specific
+ operations. Both the amd64 and x86 front ends (guests) indirectly
+ call these functions via guest helper calls. By putting them here,
+ code duplication is avoided. Some of these functions are tricky
+ and hard to verify, so there is much to be said for only having one
+ copy thereof.
+*/
+
+#include "libvex_basictypes.h"
+
+#include "main/vex_util.h"
+#include "guest-generic/g_generic_x87.h"
+
+
+/* 80 and 64-bit floating point formats:
+
+ 80-bit:
+
+ S 0 0-------0 zero
+ S 0 0X------X denormals
+ S 1-7FFE 1X------X normals (all normals have leading 1)
+ S 7FFF 10------0 infinity
+ S 7FFF 10X-----X snan
+ S 7FFF 11X-----X qnan
+
+ S is the sign bit. For runs X----X, at least one of the Xs must be
+ nonzero. Exponent is 15 bits, fractional part is 63 bits, and
+ there is an explicitly represented leading 1, and a sign bit,
+ giving 80 in total.
+
+ 64-bit avoids the confusion of an explicitly represented leading 1
+ and so is simpler:
+
+ S 0 0------0 zero
+ S 0 X------X denormals
+ S 1-7FE any normals
+ S 7FF 0------0 infinity
+ S 7FF 0X-----X snan
+ S 7FF 1X-----X qnan
+
+ Exponent is 11 bits, fractional part is 52 bits, and there is a
+ sign bit, giving 64 in total.
+*/
+
+
+static inline UInt read_bit_array ( UChar* arr, UInt n )
+{
+ UChar c = arr[n >> 3];
+ c >>= (n&7);
+ return c & 1;
+}
+
+static inline void write_bit_array ( UChar* arr, UInt n, UInt b )
+{
+ UChar c = arr[n >> 3];
+ c = toUChar( c & ~(1 << (n&7)) );
+ c = toUChar( c | ((b&1) << (n&7)) );
+ arr[n >> 3] = c;
+}
+
+/* Convert an IEEE754 double (64-bit) into an x87 extended double
+ (80-bit), mimicing the hardware fairly closely. Both numbers are
+ stored little-endian. Limitations, all of which could be fixed,
+ given some level of hassle:
+
+ * Identity of NaNs is not preserved.
+
+ See comments in the code for more details.
+*/
+void convert_f64le_to_f80le ( /*IN*/UChar* f64, /*OUT*/UChar* f80 )
+{
+ Bool mantissaIsZero;
+ Int bexp, i, j, shift;
+ UChar sign;
+
+ sign = toUChar( (f64[7] >> 7) & 1 );
+ bexp = (f64[7] << 4) | ((f64[6] >> 4) & 0x0F);
+ bexp &= 0x7FF;
+
+ mantissaIsZero = False;
+ if (bexp == 0 || bexp == 0x7FF) {
+ /* We'll need to know whether or not the mantissa (bits 51:0) is
+ all zeroes in order to handle these cases. So figure it
+ out. */
+ mantissaIsZero
+ = toBool(
+ (f64[6] & 0x0F) == 0
+ && f64[5] == 0 && f64[4] == 0 && f64[3] == 0
+ && f64[2] == 0 && f64[1] == 0 && f64[0] == 0
+ );
+ }
+
+ /* If the exponent is zero, either we have a zero or a denormal.
+ Produce a zero. This is a hack in that it forces denormals to
+ zero. Could do better. */
+ if (bexp == 0) {
+ f80[9] = toUChar( sign << 7 );
+ f80[8] = f80[7] = f80[6] = f80[5] = f80[4]
+ = f80[3] = f80[2] = f80[1] = f80[0] = 0;
+
+ if (mantissaIsZero)
+ /* It really is zero, so that's all we can do. */
+ return;
+
+ /* There is at least one 1-bit in the mantissa. So it's a
+ potentially denormalised double -- but we can produce a
+ normalised long double. Count the leading zeroes in the
+ mantissa so as to decide how much to bump the exponent down
+ by. Note, this is SLOW. */
+ shift = 0;
+ for (i = 51; i >= 0; i--) {
+ if (read_bit_array(f64, i))
+ break;
+ shift++;
+ }
+
+ /* and copy into place as many bits as we can get our hands on. */
+ j = 63;
+ for (i = 51 - shift; i >= 0; i--) {
+ write_bit_array( f80, j,
+ read_bit_array( f64, i ) );
+ j--;
+ }
+
+ /* Set the exponent appropriately, and we're done. */
+ bexp -= shift;
+ bexp += (16383 - 1023);
+ f80[9] = toUChar( (sign << 7) | ((bexp >> 8) & 0xFF) );
+ f80[8] = toUChar( bexp & 0xFF );
+ return;
+ }
+
+ /* If the exponent is 7FF, this is either an Infinity, a SNaN or
+ QNaN, as determined by examining bits 51:0, thus:
+ 0 ... 0 Inf
+ 0X ... X SNaN
+ 1X ... X QNaN
+ where at least one of the Xs is not zero.
+ */
+ if (bexp == 0x7FF) {
+ if (mantissaIsZero) {
+ /* Produce an appropriately signed infinity:
+ S 1--1 (15) 1 0--0 (63)
+ */
+ f80[9] = toUChar( (sign << 7) | 0x7F );
+ f80[8] = 0xFF;
+ f80[7] = 0x80;
+ f80[6] = f80[5] = f80[4] = f80[3]
+ = f80[2] = f80[1] = f80[0] = 0;
+ return;
+ }
+ /* So it's either a QNaN or SNaN. Distinguish by considering
+ bit 51. Note, this destroys all the trailing bits
+ (identity?) of the NaN. IEEE754 doesn't require preserving
+ these (it only requires that there be one QNaN value and one
+ SNaN value), but x87 does seem to have some ability to
+ preserve them. Anyway, here, the NaN's identity is
+ destroyed. Could be improved. */
+ if (f64[6] & 8) {
+ /* QNaN. Make a QNaN:
+ S 1--1 (15) 1 1--1 (63)
+ */
+ f80[9] = toUChar( (sign << 7) | 0x7F );
+ f80[8] = 0xFF;
+ f80[7] = 0xFF;
+ f80[6] = f80[5] = f80[4] = f80[3]
+ = f80[2] = f80[1] = f80[0] = 0xFF;
+ } else {
+ /* SNaN. Make a SNaN:
+ S 1--1 (15) 0 1--1 (63)
+ */
+ f80[9] = toUChar( (sign << 7) | 0x7F );
+ f80[8] = 0xFF;
+ f80[7] = 0x7F;
+ f80[6] = f80[5] = f80[4] = f80[3]
+ = f80[2] = f80[1] = f80[0] = 0xFF;
+ }
+ return;
+ }
+
+ /* It's not a zero, denormal, infinity or nan. So it must be a
+ normalised number. Rebias the exponent and build the new
+ number. */
+ bexp += (16383 - 1023);
+
+ f80[9] = toUChar( (sign << 7) | ((bexp >> 8) & 0xFF) );
+ f80[8] = toUChar( bexp & 0xFF );
+ f80[7] = toUChar( (1 << 7) | ((f64[6] << 3) & 0x78)
+ | ((f64[5] >> 5) & 7) );
+ f80[6] = toUChar( ((f64[5] << 3) & 0xF8) | ((f64[4] >> 5) & 7) );
+ f80[5] = toUChar( ((f64[4] << 3) & 0xF8) | ((f64[3] >> 5) & 7) );
+ f80[4] = toUChar( ((f64[3] << 3) & 0xF8) | ((f64[2] >> 5) & 7) );
+ f80[3] = toUChar( ((f64[2] << 3) & 0xF8) | ((f64[1] >> 5) & 7) );
+ f80[2] = toUChar( ((f64[1] << 3) & 0xF8) | ((f64[0] >> 5) & 7) );
+ f80[1] = toUChar( ((f64[0] << 3) & 0xF8) );
+ f80[0] = toUChar( 0 );
+}
+
+
+/* Convert an x87 extended double (80-bit) into an IEEE 754 double
+ (64-bit), mimicking the hardware fairly closely. Both numbers are
+ stored little-endian. Limitations, both of which could be fixed,
+ given some level of hassle:
+
+ * Rounding following truncation could be a bit better.
+
+ * Identity of NaNs is not preserved.
+
+ See comments in the code for more details.
+*/
+void convert_f80le_to_f64le ( /*IN*/UChar* f80, /*OUT*/UChar* f64 )
+{
+ Bool isInf;
+ Int bexp, i, j;
+ UChar sign;
+
+ sign = toUChar((f80[9] >> 7) & 1);
+ bexp = (((UInt)f80[9]) << 8) | (UInt)f80[8];
+ bexp &= 0x7FFF;
+
+ /* If the exponent is zero, either we have a zero or a denormal.
+ But an extended precision denormal becomes a double precision
+ zero, so in either case, just produce the appropriately signed
+ zero. */
+ if (bexp == 0) {
+ f64[7] = toUChar(sign << 7);
+ f64[6] = f64[5] = f64[4] = f64[3] = f64[2] = f64[1] = f64[0] = 0;
+ return;
+ }
+
+ /* If the exponent is 7FFF, this is either an Infinity, a SNaN or
+ QNaN, as determined by examining bits 62:0, thus:
+ 0 ... 0 Inf
+ 0X ... X SNaN
+ 1X ... X QNaN
+ where at least one of the Xs is not zero.
+ */
+ if (bexp == 0x7FFF) {
+ isInf = toBool(
+ (f80[7] & 0x7F) == 0
+ && f80[6] == 0 && f80[5] == 0 && f80[4] == 0
+ && f80[3] == 0 && f80[2] == 0 && f80[1] == 0
+ && f80[0] == 0
+ );
+ if (isInf) {
+ if (0 == (f80[7] & 0x80))
+ goto wierd_NaN;
+ /* Produce an appropriately signed infinity:
+ S 1--1 (11) 0--0 (52)
+ */
+ f64[7] = toUChar((sign << 7) | 0x7F);
+ f64[6] = 0xF0;
+ f64[5] = f64[4] = f64[3] = f64[2] = f64[1] = f64[0] = 0;
+ return;
+ }
+ /* So it's either a QNaN or SNaN. Distinguish by considering
+ bit 62. Note, this destroys all the trailing bits
+ (identity?) of the NaN. IEEE754 doesn't require preserving
+ these (it only requires that there be one QNaN value and one
+ SNaN value), but x87 does seem to have some ability to
+ preserve them. Anyway, here, the NaN's identity is
+ destroyed. Could be improved. */
+ if (f80[8] & 0x40) {
+ /* QNaN. Make a QNaN:
+ S 1--1 (11) 1 1--1 (51)
+ */
+ f64[7] = toUChar((sign << 7) | 0x7F);
+ f64[6] = 0xFF;
+ f64[5] = f64[4] = f64[3] = f64[2] = f64[1] = f64[0] = 0xFF;
+ } else {
+ /* SNaN. Make a SNaN:
+ S 1--1 (11) 0 1--1 (51)
+ */
+ f64[7] = toUChar((sign << 7) | 0x7F);
+ f64[6] = 0xF7;
+ f64[5] = f64[4] = f64[3] = f64[2] = f64[1] = f64[0] = 0xFF;
+ }
+ return;
+ }
+
+ /* If it's not a Zero, NaN or Inf, and the integer part (bit 62) is
+ zero, the x87 FPU appears to consider the number denormalised
+ and converts it to a QNaN. */
+ if (0 == (f80[7] & 0x80)) {
+ wierd_NaN:
+ /* Strange hardware QNaN:
+ S 1--1 (11) 1 0--0 (51)
+ */
+ /* On a PIII, these QNaNs always appear with sign==1. I have
+ no idea why. */
+ f64[7] = (1 /*sign*/ << 7) | 0x7F;
+ f64[6] = 0xF8;
+ f64[5] = f64[4] = f64[3] = f64[2] = f64[1] = f64[0] = 0;
+ return;
+ }
+
+ /* It's not a zero, denormal, infinity or nan. So it must be a
+ normalised number. Rebias the exponent and consider. */
+ bexp -= (16383 - 1023);
+ if (bexp >= 0x7FF) {
+ /* It's too big for a double. Construct an infinity. */
+ f64[7] = toUChar((sign << 7) | 0x7F);
+ f64[6] = 0xF0;
+ f64[5] = f64[4] = f64[3] = f64[2] = f64[1] = f64[0] = 0;
+ return;
+ }
+
+ if (bexp <= 0) {
+ /* It's too small for a normalised double. First construct a
+ zero and then see if it can be improved into a denormal. */
+ f64[7] = toUChar(sign << 7);
+ f64[6] = f64[5] = f64[4] = f64[3] = f64[2] = f64[1] = f64[0] = 0;
+
+ if (bexp < -52)
+ /* Too small even for a denormal. */
+ return;
+
+ /* Ok, let's make a denormal. Note, this is SLOW. */
+ /* Copy bits 63, 62, 61, etc of the src mantissa into the dst,
+ indexes 52+bexp, 51+bexp, etc, until k+bexp < 0. */
+ /* bexp is in range -52 .. 0 inclusive */
+ for (i = 63; i >= 0; i--) {
+ j = i - 12 + bexp;
+ if (j < 0) break;
+ /* We shouldn't really call vassert from generated code. */
+ vassert(j >= 0 && j < 52);
+ write_bit_array ( f64,
+ j,
+ read_bit_array ( f80, i ) );
+ }
+ /* and now we might have to round ... */
+ if (read_bit_array(f80, 10+1 - bexp) == 1)
+ goto do_rounding;
+
+ return;
+ }
+
+ /* Ok, it's a normalised number which is representable as a double.
+ Copy the exponent and mantissa into place. */
+ /*
+ for (i = 0; i < 52; i++)
+ write_bit_array ( f64,
+ i,
+ read_bit_array ( f80, i+11 ) );
+ */
+ f64[0] = toUChar( (f80[1] >> 3) | (f80[2] << 5) );
+ f64[1] = toUChar( (f80[2] >> 3) | (f80[3] << 5) );
+ f64[2] = toUChar( (f80[3] >> 3) | (f80[4] << 5) );
+ f64[3] = toUChar( (f80[4] >> 3) | (f80[5] << 5) );
+ f64[4] = toUChar( (f80[5] >> 3) | (f80[6] << 5) );
+ f64[5] = toUChar( (f80[6] >> 3) | (f80[7] << 5) );
+
+ f64[6] = toUChar( ((bexp << 4) & 0xF0) | ((f80[7] >> 3) & 0x0F) );
+
+ f64[7] = toUChar( (sign << 7) | ((bexp >> 4) & 0x7F) );
+
+ /* Now consider any rounding that needs to happen as a result of
+ truncating the mantissa. */
+ if (f80[1] & 4) /* read_bit_array(f80, 10) == 1) */ {
+
+ /* If the bottom bits of f80 are "100 0000 0000", then the
+ infinitely precise value is deemed to be mid-way between the
+ two closest representable values. Since we're doing
+ round-to-nearest (the default mode), in that case it is the
+ bit immediately above which indicates whether we should round
+ upwards or not -- if 0, we don't. All that is encapsulated
+ in the following simple test. */
+ if ((f80[1] & 0xF) == 4/*0100b*/ && f80[0] == 0)
+ return;
+
+ do_rounding:
+ /* Round upwards. This is a kludge. Once in every 2^24
+ roundings (statistically) the bottom three bytes are all 0xFF
+ and so we don't round at all. Could be improved. */
+ if (f64[0] != 0xFF) {
+ f64[0]++;
+ }
+ else
+ if (f64[0] == 0xFF && f64[1] != 0xFF) {
+ f64[0] = 0;
+ f64[1]++;
+ }
+ else
+ if (f64[0] == 0xFF && f64[1] == 0xFF && f64[2] != 0xFF) {
+ f64[0] = 0;
+ f64[1] = 0;
+ f64[2]++;
+ }
+ /* else we don't round, but we should. */
+ }
+}
+
+
+/*---------------------------------------------------------------*/
+/*--- end guest-generic/h_generic_x87.c ---*/
+/*---------------------------------------------------------------*/