sh: Subnormal double to float conversion

This patch adds support for the SH4 to convert a subnormal double
into a float by catching the FPE and implementing the FCNVDS
instruction in software.

Signed-off-by: Carl Shaw <carl.shaw@st.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/kernel/cpu/sh4/fpu.c

@@ -36,7 +36,7 @@ extern unsigned long int float32_add(unsigned long int a, unsigned long int b);
 extern unsigned long long float64_sub(unsigned long long a,
 				      unsigned long long b);
 extern unsigned long int float32_sub(unsigned long int a, unsigned long int b);
-
+extern unsigned long int float64_to_float32(unsigned long long a);
 static unsigned int fpu_exception_flags;
 
 /*
@@ -415,6 +415,29 @@ static int ieee_fpe_handler(struct pt_regs *regs)
 		} else
 			return 0;
 
+		regs->pc = nextpc;
+		return 1;
+	} else if ((finsn & 0xf0bd) == 0xf0bd) {
+		/* fcnvds - double to single precision convert */
+		struct task_struct *tsk = current;
+		int m;
+		unsigned int hx;
+
+		m = (finsn >> 9) & 0x7;
+		hx = tsk->thread.fpu.hard.fp_regs[m];
+
+		if ((tsk->thread.fpu.hard.fpscr & FPSCR_CAUSE_ERROR)
+			&& ((hx & 0x7fffffff) < 0x00100000)) {
+			/* subnormal double to float conversion */
+			long long llx;
+
+			llx = ((long long)tsk->thread.fpu.hard.fp_regs[m] << 32)
+			    | tsk->thread.fpu.hard.fp_regs[m + 1];
+
+			tsk->thread.fpu.hard.fpul = float64_to_float32(llx);
+		} else
+			return 0;
+
 		regs->pc = nextpc;
 		return 1;
 	}

arch/sh/kernel/cpu/sh4/softfloat.c

@@ -85,6 +85,7 @@ float64 float64_div(float64 a, float64 b);
 float32 float32_div(float32 a, float32 b);
 float32 float32_mul(float32 a, float32 b);
 float64 float64_mul(float64 a, float64 b);
+float32 float64_to_float32(float64 a);
 inline void add128(bits64 a0, bits64 a1, bits64 b0, bits64 b1, bits64 * z0Ptr,
 		   bits64 * z1Ptr);
 inline void sub128(bits64 a0, bits64 a1, bits64 b0, bits64 b1, bits64 * z0Ptr,
@@ -890,3 +891,31 @@ float64 float64_mul(float64 a, float64 b)
 	}
 	return roundAndPackFloat64(zSign, zExp, zSig0);
 }
+
+/*
+ * -------------------------------------------------------------------------------
+ *  Returns the result of converting the double-precision floating-point value
+ *  `a' to the single-precision floating-point format.  The conversion is
+ *  performed according to the IEC/IEEE Standard for Binary Floating-point
+ *  Arithmetic.
+ *  -------------------------------------------------------------------------------
+ *  */
+float32 float64_to_float32(float64 a)
+{
+    flag aSign;
+    int16 aExp;
+    bits64 aSig;
+    bits32 zSig;
+
+    aSig = extractFloat64Frac( a );
+    aExp = extractFloat64Exp( a );
+    aSign = extractFloat64Sign( a );
+
+    shift64RightJamming( aSig, 22, &aSig );
+    zSig = aSig;
+    if ( aExp || zSig ) {
+        zSig |= 0x40000000;
+        aExp -= 0x381;
+    }
+    return roundAndPackFloat32(aSign, aExp, zSig);
+}