[POWERPC] Emulate power5 popcntb instruction

In an attempt to make it easier for a power5 optimized app to run on a
power4 or a 970 or random earlier machine, this provides emulation of
the popcntb instruction.
Signed-off-by: Will Schmidt <will_schmidt@vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/traps.c

@@ -598,6 +598,9 @@ static void parse_fpe(struct pt_regs *regs)
 #define INST_STSWI		0x7c0005aa
 #define INST_STSWX		0x7c00052a
 
+#define INST_POPCNTB		0x7c0000f4
+#define INST_POPCNTB_MASK	0xfc0007fe
+
 static int emulate_string_inst(struct pt_regs *regs, u32 instword)
 {
 	u8 rT = (instword >> 21) & 0x1f;
@@ -666,6 +669,23 @@ static int emulate_string_inst(struct pt_regs *regs, u32 instword)
 	return 0;
 }
 
+static int emulate_popcntb_inst(struct pt_regs *regs, u32 instword)
+{
+	u32 ra,rs;
+	unsigned long tmp;
+
+	ra = (instword >> 16) & 0x1f;
+	rs = (instword >> 21) & 0x1f;
+
+	tmp = regs->gpr[rs];
+	tmp = tmp - ((tmp >> 1) & 0x5555555555555555ULL);
+	tmp = (tmp & 0x3333333333333333ULL) + ((tmp >> 2) & 0x3333333333333333ULL);
+	tmp = (tmp + (tmp >> 4)) & 0x0f0f0f0f0f0f0f0fULL;
+	regs->gpr[ra] = tmp;
+
+	return 0;
+}
+
 static int emulate_instruction(struct pt_regs *regs)
 {
 	u32 instword;
@@ -703,6 +723,11 @@ static int emulate_instruction(struct pt_regs *regs)
 	if ((instword & INST_STRING_GEN_MASK) == INST_STRING)
 		return emulate_string_inst(regs, instword);
 
+	/* Emulate the popcntb (Population Count Bytes) instruction. */
+	if ((instword & INST_POPCNTB_MASK) == INST_POPCNTB) {
+		return emulate_popcntb_inst(regs, instword);
+	}
+
 	return -EINVAL;
 }