libgcc/m68k: Fixes for soft float

Return correctly signed zero on float and double divide underflow

Return positive qNaN instead of negative.

Fix __fixxfsi which was off by a factor of two. Simplify the code
having realized that the lower 32 bits of the significand can never
appear in the results.

Signed-off-by: Keith Packard <keithp@keithp.com>

Author: keith-packard

libgcc/config/m68k/fpgnulib.c

@@ -475,6 +475,29 @@ __extenddfxf2 (double d)
     exp = EXPXMASK;
   ldl.l.upper |= exp << 16;
   ldl.l.middle = HIDDENX;
+
+  /* Recover from a denorm. */
+  if (exp == -EXCESSD + EXCESSX)
+    {
+      exp++;
+      while ((dl.l.upper & HIDDEND) == 0)
+	{
+	  exp--;
+	  dl.l.upper = (dl.l.upper << 1) | (dl.l.lower >> 31);
+	  dl.l.lower = dl.l.lower << 1;
+	}
+    }
+
+  /* Handle inf and NaN */
+  else if (exp == EXPDMASK - EXCESSD + EXCESSX)
+    {
+      exp = EXPXMASK;
+      /* No hidden one bit for INF */
+      if (dl.l.upper == 0 && dl.l.lower == 0)
+	ldl.l.middle = 0;
+    }
+
+  ldl.l.upper |= exp << 16;
   /* 31-20: # mantissa bits in ldl.l.middle - # mantissa bits in dl.l.upper */
   ldl.l.middle |= (dl.l.upper & MANTDMASK) << (31 - 20);
   /* 1+20: explicit-integer-bit + # mantissa bits in dl.l.upper */
@@ -585,36 +608,27 @@ __fixxfsi (long double a)
 {
   union long_double_long ldl;
   long exp;
-  long l;
 
   ldl.ld = a;
 
   exp = EXPX (ldl);
   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.  */

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$exit:
 #endif
 	beq	2f		| if not loop back
 	bra	1b              |
+	movel	a0,d7
 	bra	Ld$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