[Qemu-devel] [PATCH v2] target-arm: fix VSHLL Neon instruction.

* [Qemu-devel] [PATCH v2] target-arm: fix VSHLL Neon instruction.
@ 2011-02-09 12:19 Christophe Lyon
  2011-02-09 14:23 ` Peter Maydell
  0 siblings, 1 reply; 3+ messages in thread
From: Christophe Lyon @ 2011-02-09 12:19 UTC (permalink / raw)
  To: qemu-devel


Fix bit mask used when widening the result of shift on narrow input.

Signed-off-by: Christophe Lyon <christophe.lyon@st.com>
---
 target-arm/translate.c |   18 +++++++++++++++---
 1 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/target-arm/translate.c b/target-arm/translate.c
index b694eed..16c61f1 100644
--- a/target-arm/translate.c
+++ b/target-arm/translate.c
@@ -4882,16 +4882,28 @@ static int disas_neon_data_insn(CPUState * env, DisasContext *s, uint32_t insn)
                         /* The shift is less than the width of the source
                            type, so we can just shift the whole register.  */
                         tcg_gen_shli_i64(cpu_V0, cpu_V0, shift);
+                        /* Widen the result of shift: we need to clear
+                         * the potential overflow bits resulting from
+                         * left bits of the narrow input appearing as
+                         * right bits of left the neighbour narrow
+                         * input.  */
                         if (size < 2 || !u) {
                             uint64_t imm64;
                             if (size == 0) {
                                 imm = (0xffu >> (8 - shift));
                                 imm |= imm << 16;
-                            } else {
+                            } else if (size == 1) {
                                 imm = 0xffff >> (16 - shift);
+                            } else {
+                                /* size == 2 */
+                                imm = 0xffffffff >> (32 - shift);
+                            }
+                            if (size < 2) {
+                                imm64 = imm | (((uint64_t)imm) << 32);
+                            } else {
+                                imm64 = imm;
                             }
-                            imm64 = imm | (((uint64_t)imm) << 32);
-                            tcg_gen_andi_i64(cpu_V0, cpu_V0, imm64);
+                            tcg_gen_andi_i64(cpu_V0, cpu_V0, ~imm64);
                         }
                     }
                     neon_store_reg64(cpu_V0, rd + pass);
-- 
1.7.2.3

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