target/arm: Make asimd_imm_const() public

The function asimd_imm_const() in translate-neon.c is an
implementation of the pseudocode AdvSIMDExpandImm(), which we will
also want for MVE.  Move the implementation to translate.c, with a
prototype in translate.h.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210628135835.6690-4-peter.maydell@linaro.org

1 files changed, 57 insertions, 0 deletions

diff --git a/target/arm/translate.c b/target/arm/translate.c
index a0c6cfa902..95ceb24ec3 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -90,6 +90,63 @@ void arm_translate_init(void)
     a64_translate_init();
 }
 
+uint64_t asimd_imm_const(uint32_t imm, int cmode, int op)
+{
+    /* Expand the encoded constant as per AdvSIMDExpandImm pseudocode */
+    switch (cmode) {
+    case 0: case 1:
+        /* no-op */
+        break;
+    case 2: case 3:
+        imm <<= 8;
+        break;
+    case 4: case 5:
+        imm <<= 16;
+        break;
+    case 6: case 7:
+        imm <<= 24;
+        break;
+    case 8: case 9:
+        imm |= imm << 16;
+        break;
+    case 10: case 11:
+        imm = (imm << 8) | (imm << 24);
+        break;
+    case 12:
+        imm = (imm << 8) | 0xff;
+        break;
+    case 13:
+        imm = (imm << 16) | 0xffff;
+        break;
+    case 14:
+        if (op) {
+            /*
+             * This is the only case where the top and bottom 32 bits
+             * of the encoded constant differ.
+             */
+            uint64_t imm64 = 0;
+            int n;
+
+            for (n = 0; n < 8; n++) {
+                if (imm & (1 << n)) {
+                    imm64 |= (0xffULL << (n * 8));
+                }
+            }
+            return imm64;
+        }
+        imm |= (imm << 8) | (imm << 16) | (imm << 24);
+        break;
+    case 15:
+        imm = ((imm & 0x80) << 24) | ((imm & 0x3f) << 19)
+            | ((imm & 0x40) ? (0x1f << 25) : (1 << 30));
+        break;
+    }
+    if (op) {
+        imm = ~imm;
+    }
+    return dup_const(MO_32, imm);
+}
+
 /* Generate a label used for skipping this instruction */
 void arm_gen_condlabel(DisasContext *s)
 {