target-ppc: Introduce DFP Helper Utilities

Add a new file (dfp_helper.c) to the PowerPC implementation for Decimal Floating
Point (DFP) emulation.  This first version of the file declares a structure that
will be used by DFP helpers.  It also implements utilities that will initialize
such a structure for either a long (64 bit) DFP instruction or an extended (128
bit, aka "quad") instruction.

Some utility functions are annotated with the unused attribute in order to preserve
build bisection.

Signed-off-by: Tom Musta <tommusta@gmail.com>
[agraf: Add never reached assert on dfp_prepare_rounding_mode()]
Signed-off-by: Alexander Graf <agraf@suse.de>

2 files changed, 133 insertions, 0 deletions

diff --git a/target-ppc/Makefile.objs b/target-ppc/Makefile.objs
index 3cb23e0f11..a7ae392cc0 100644
--- a/target-ppc/Makefile.objs
+++ b/target-ppc/Makefile.objs
@@ -6,6 +6,7 @@ obj-$(TARGET_PPC64) += mmu-hash64.o arch_dump.o
 endif
 obj-$(CONFIG_KVM) += kvm.o kvm_ppc.o
 obj-$(call lnot,$(CONFIG_KVM)) += kvm-stub.o
+obj-y += dfp_helper.o
 obj-y += excp_helper.o
 obj-y += fpu_helper.o
 obj-y += int_helper.o
diff --git a/target-ppc/dfp_helper.c b/target-ppc/dfp_helper.c
new file mode 100644
index 0000000000..b4f01395f7
--- /dev/null
+++ b/target-ppc/dfp_helper.c
@@ -0,0 +1,132 @@
+/*
+ *  PowerPC Decimal Floating Point (DPF) emulation helpers for QEMU.
+ *
+ *  Copyright (c) 2014 IBM Corporation.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library 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.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "cpu.h"
+#include "exec/helper-proto.h"
+
+#define DECNUMDIGITS 34
+#include "libdecnumber/decContext.h"
+#include "libdecnumber/decNumber.h"
+#include "libdecnumber/dpd/decimal32.h"
+#include "libdecnumber/dpd/decimal64.h"
+#include "libdecnumber/dpd/decimal128.h"
+
+#if defined(HOST_WORDS_BIGENDIAN)
+#define HI_IDX 0
+#define LO_IDX 1
+#else
+#define HI_IDX 1
+#define LO_IDX 0
+#endif
+
+struct PPC_DFP {
+    CPUPPCState *env;
+    uint64_t t64[2], a64[2], b64[2];
+    decNumber t, a, b;
+    decContext context;
+    uint8_t crbf;
+};
+
+static void dfp_prepare_rounding_mode(decContext *context, uint64_t fpscr)
+{
+    enum rounding rnd;
+
+    switch ((fpscr >> 32) & 0x7) {
+    case 0:
+        rnd = DEC_ROUND_HALF_EVEN;
+        break;
+    case 1:
+        rnd = DEC_ROUND_DOWN;
+        break;
+    case 2:
+         rnd = DEC_ROUND_CEILING;
+         break;
+    case 3:
+         rnd = DEC_ROUND_FLOOR;
+         break;
+    case 4:
+         rnd = DEC_ROUND_HALF_UP;
+         break;
+    case 5:
+         rnd = DEC_ROUND_HALF_DOWN;
+         break;
+    case 6:
+         rnd = DEC_ROUND_UP;
+         break;
+    case 7:
+         rnd = DEC_ROUND_05UP;
+         break;
+    default:
+        g_assert_not_reached();
+    }
+
+    decContextSetRounding(context, rnd);
+}
+
+__attribute__ ((unused))
+static void dfp_prepare_decimal64(struct PPC_DFP *dfp, uint64_t *a,
+                uint64_t *b, CPUPPCState *env)
+{
+    decContextDefault(&dfp->context, DEC_INIT_DECIMAL64);
+    dfp_prepare_rounding_mode(&dfp->context, env->fpscr);
+    dfp->env = env;
+
+    if (a) {
+        dfp->a64[0] = *a;
+        decimal64ToNumber((decimal64 *)dfp->a64, &dfp->a);
+    } else {
+        dfp->a64[0] = 0;
+        decNumberZero(&dfp->a);
+    }
+
+    if (b) {
+        dfp->b64[0] = *b;
+        decimal64ToNumber((decimal64 *)dfp->b64, &dfp->b);
+    } else {
+        dfp->b64[0] = 0;
+        decNumberZero(&dfp->b);
+    }
+}
+
+__attribute__ ((unused))
+static void dfp_prepare_decimal128(struct PPC_DFP *dfp, uint64_t *a,
+                uint64_t *b, CPUPPCState *env)
+{
+    decContextDefault(&dfp->context, DEC_INIT_DECIMAL128);
+    dfp_prepare_rounding_mode(&dfp->context, env->fpscr);
+    dfp->env = env;
+
+    if (a) {
+        dfp->a64[0] = a[HI_IDX];
+        dfp->a64[1] = a[LO_IDX];
+        decimal128ToNumber((decimal128 *)dfp->a64, &dfp->a);
+    } else {
+        dfp->a64[0] = dfp->a64[1] = 0;
+        decNumberZero(&dfp->a);
+    }
+
+    if (b) {
+        dfp->b64[0] = b[HI_IDX];
+        dfp->b64[1] = b[LO_IDX];
+        decimal128ToNumber((decimal128 *)dfp->b64, &dfp->b);
+    } else {
+        dfp->b64[0] = dfp->b64[1] = 0;
+        decNumberZero(&dfp->b);
+    }
+}