I thought I had sent all of my m68k soft float fixes along last year, but it looks like I managed to leave some out. I had been building my toolchain from a private repo (oops), which masked my mistake. We're fixing that by automatically building toolchains from upstream source with a list of patches now, so this "shouldn't" happen again. Now to drive that list of patches to zero.
From 1a3e403603f5a687724c7e2f6625debc3d23d934 Mon Sep 17 00:00:00 2001
From: Keith Packard <kei...@keithp.com>
Date: Sun, 29 Dec 2024 01:42:29 -0800
Subject: [PATCH] libgcc/m68k: Fixes for soft float
Fix __extenddfxf2:
* Remove bogus denorm handling block which would never execute --
the converted exp value is always positive as EXCESSX > EXCESSD.
* Compute the whole significand in dl instead of doing part of it in
ldl.
* Mask off exponent from dl.l.upper so the denorm shift test
works.
* Insert the hidden one bit into dl.l.upper as needed.
Fix __truncxfdf2 denorm handling. All that is required is to shift the
significand right by the correct amount; it already has all of the
necessary bits set including the explicit one. Compute the shift
amount, then perform the wide shift across both elements of the
significand.
Fix __fixxfsi:
* The value was off by a factor of two as the significand contains
32 bits, not 31 so we need to shift by one more than the equivalent
code in __fixdfsi.
* Simplify the code having realized that the lower 32 bits of the
significand can never appear in the results.
Return positive qNaN instead of negative. For floats, qNaN is 0x7fff_ffff. For
doubles, qNaN is 0x7fff_ffff_ffff_ffff.
Return correctly signed zero on float and double divide underflow. This means
that Ld$underflow now expects d7 to contain the sign bit, just like the other
return paths.
Signed-off-by: Keith Packard <kei...@keithp.com>
---
libgcc/config/m68k/fpgnulib.c | 78 ++++++++++++++++-------------------
libgcc/config/m68k/lb1sf68.S | 13 ++++--
2 files changed, 45 insertions(+), 46 deletions(-)
diff --git a/libgcc/config/m68k/fpgnulib.c b/libgcc/config/m68k/fpgnulib.c
index 70bfd442d75..a7d4258dff0 100644
--- a/libgcc/config/m68k/fpgnulib.c
+++ b/libgcc/config/m68k/fpgnulib.c
@@ -449,34 +449,37 @@ __extenddfxf2 (double d)
}
exp = EXPD (dl) - EXCESSD + EXCESSX;
- /* Check for underflow and denormals. */
- if (exp < 0)
+
+ dl.l.upper &= MANTDMASK;
+
+ /* Recover from a denorm. */
+ if (exp == -EXCESSD + EXCESSX)
{
- if (exp < -53)
- {
- ldl.l.middle = 0;
- ldl.l.lower = 0;
- }
- else if (exp < -30)
- {
- ldl.l.lower = (ldl.l.middle & MANTXMASK) >> ((1 - exp) - 32);
- ldl.l.middle &= ~MANTXMASK;
- }
- else
+ exp++;
+ while ((dl.l.upper & HIDDEND) == 0)
{
- ldl.l.lower >>= 1 - exp;
- ldl.l.lower |= (ldl.l.middle & MANTXMASK) << (32 - (1 - exp));
- ldl.l.middle = (ldl.l.middle & ~MANTXMASK) | (ldl.l.middle & MANTXMASK >> (1 - exp));
+ exp--;
+ dl.l.upper = (dl.l.upper << 1) | (dl.l.lower >> 31);
+ dl.l.lower = dl.l.lower << 1;
}
- exp = 0;
}
+
/* Handle inf and NaN */
- if (exp == EXPDMASK - EXCESSD + EXCESSX)
- exp = EXPXMASK;
+ else if (exp == EXPDMASK - EXCESSD + EXCESSX)
+ {
+ exp = EXPXMASK;
+ /* Add hidden one bit for NaN */
+ if (dl.l.upper != 0 || dl.l.lower != 0)
+ dl.l.upper |= HIDDEND;
+ }
+ else
+ {
+ dl.l.upper |= HIDDEND;
+ }
+
ldl.l.upper |= exp << 16;
- ldl.l.middle = HIDDENX;
/* 31-20: # mantissa bits in ldl.l.middle - # mantissa bits in dl.l.upper */
- ldl.l.middle |= (dl.l.upper & MANTDMASK) << (31 - 20);
+ ldl.l.middle = dl.l.upper << (31 - 20);
/* 1+20: explicit-integer-bit + # mantissa bits in dl.l.upper */
ldl.l.middle |= dl.l.lower >> (1 + 20);
/* 32 - 21: # bits of dl.l.lower in ldl.l.middle */
@@ -508,21 +511,21 @@ __truncxfdf2 (long double ld)
/* Check for underflow and denormals. */
if (exp <= 0)
{
- if (exp < -53)
+ long shift = 1 - exp;
+ if (shift > 52)
{
ldl.l.middle = 0;
ldl.l.lower = 0;
}
- else if (exp < -30)
+ else if (shift >= 32)
{
- ldl.l.lower = (ldl.l.middle & MANTXMASK) >> ((1 - exp) - 32);
- ldl.l.middle &= ~MANTXMASK;
+ ldl.l.lower = (ldl.l.middle) >> (shift - 32);
+ ldl.l.middle = 0;
}
else
{
- ldl.l.lower >>= 1 - exp;
- ldl.l.lower |= (ldl.l.middle & MANTXMASK) << (32 - (1 - exp));
- ldl.l.middle = (ldl.l.middle & ~MANTXMASK) | (ldl.l.middle & MANTXMASK >> (1 - exp));
+ ldl.l.lower = (ldl.l.middle << (32 - shift)) | (ldl.l.lower >> shift);
+ ldl.l.middle = ldl.l.middle >> shift;
}
exp = 0;
}
@@ -585,7 +588,6 @@ __fixxfsi (long double a)
{
union long_double_long ldl;
long exp;
- long l;
ldl.ld = a;
@@ -593,28 +595,20 @@ __fixxfsi (long double a)
if (exp == 0 && ldl.l.middle == 0 && ldl.l.lower == 0)
return 0;
- exp = exp - EXCESSX - 63;
+ exp = exp - EXCESSX - 32;
- if (exp > 0)
+ if (exp >= 0)
{
/* Return largest integer. */
return SIGNX (ldl) ? 0x80000000L : 0x7fffffffL;
}
- if (exp <= -64)
+ if (exp <= -32)
return 0;
- if (exp <= -32)
- {
- ldl.l.lower = ldl.l.middle >> (-exp - 32);
- }
- else if (exp < 0)
- {
- ldl.l.lower = ldl.l.lower >> -exp;
- ldl.l.lower |= ldl.l.middle << (32 + exp);
- }
+ ldl.l.middle >>= -exp;
- return SIGNX (ldl) ? -ldl.l.lower : ldl.l.lower;
+ return SIGNX (ldl) ? -ldl.l.middle : ldl.l.middle;
}
/* The remaining provide crude math support by working in double precision. */
diff --git a/libgcc/config/m68k/lb1sf68.S b/libgcc/config/m68k/lb1sf68.S
index 22f2772520c..ebec095c6e7 100644
--- a/libgcc/config/m68k/lb1sf68.S
+++ b/libgcc/config/m68k/lb1sf68.S
@@ -635,7 +635,7 @@ SYM (__modsi3):
.globl SYM (_fpCCR)
.globl $_exception_handler
-QUIET_NaN = 0xffffffff
+QUIET_NaN = 0x7fffffff
D_MAX_EXP = 0x07ff
D_BIAS = 1022
@@ -700,9 +700,10 @@ Ld$overflow:
PICJUMP $_exception_handler
Ld$underflow:
-| Return 0 and set the exception flags
+| Return a properly signed 0 and set the exception flags
movel IMM (0),d0
movel d0,d1
+ orl d7,d0
movew IMM (INEXACT_RESULT+UNDERFLOW),d7
moveq IMM (DOUBLE_FLOAT),d6
PICJUMP $_exception_handler
@@ -711,6 +712,7 @@ Ld$inop:
| Return a quiet NaN and set the exception flags
movel IMM (QUIET_NaN),d0
movel d0,d1
+ bset IMM (31),d1
movew IMM (INEXACT_RESULT+INVALID_OPERATION),d7
moveq IMM (DOUBLE_FLOAT),d6
PICJUMP $_exception_handler
@@ -2082,6 +2084,7 @@ Ldivdf$b$nf:
| If d2 == 0x7ff00000 we have to check d3.
tstl d3 |
bne Ld$inop | if d3 <> 0, b is NaN
+ movel a0,d7 | put a's sign
bra Ld$underflow | else b is +/-INFINITY, so signal underflow
Ldivdf$a$nf:
@@ -2187,6 +2190,7 @@ Lround$exit:
#endif
beq 2f | if not loop back
bra 1b |
+ movel a0,d7 | get back sign bit into d7
bra Ld$underflow | safety check, shouldn't execute '
2: orl d6,d2 | this is a trick so we don't lose '
orl d7,d3 | the bits which were flushed right
@@ -2549,7 +2553,7 @@ Lround$to$minus:
.globl SYM (_fpCCR)
.globl $_exception_handler
-QUIET_NaN = 0xffffffff
+QUIET_NaN = 0x7fffffff
SIGNL_NaN = 0x7f800001
INFINITY = 0x7f800000
@@ -2615,8 +2619,9 @@ Lf$overflow:
PICJUMP $_exception_handler
Lf$underflow:
-| Return 0 and set the exception flags
+| Return a properly signed 0 and set the exception flags
moveq IMM (0),d0
+ orl d7,d0
moveq IMM (INEXACT_RESULT+UNDERFLOW),d7
moveq IMM (SINGLE_FLOAT),d6
PICJUMP $_exception_handler
--
2.45.2
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