target/arm: Implement bfloat16 dot product (vector)

This is BFDOT for both AArch64 AdvSIMD and SVE,
and VDOT.BF16 for AArch32 NEON.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210525225817.400336-7-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 40 insertions, 0 deletions

diff --git a/target/arm/vec_helper.c b/target/arm/vec_helper.c
index e84b438340..7eefcd06ea 100644
--- a/target/arm/vec_helper.c
+++ b/target/arm/vec_helper.c
@@ -2412,3 +2412,43 @@ static void do_mmla_b(void *vd, void *vn, void *vm, void *va, uint32_t desc,
 DO_MMLA_B(gvec_smmla_b, do_smmla_b)
 DO_MMLA_B(gvec_ummla_b, do_ummla_b)
 DO_MMLA_B(gvec_usmmla_b, do_usmmla_b)
+
+/*
+ * BFloat16 Dot Product
+ */
+
+static float32 bfdotadd(float32 sum, uint32_t e1, uint32_t e2)
+{
+    /* FPCR is ignored for BFDOT and BFMMLA. */
+    float_status bf_status = {
+        .tininess_before_rounding = float_tininess_before_rounding,
+        .float_rounding_mode = float_round_to_odd_inf,
+        .flush_to_zero = true,
+        .flush_inputs_to_zero = true,
+        .default_nan_mode = true,
+    };
+    float32 t1, t2;
+
+    /*
+     * Extract each BFloat16 from the element pair, and shift
+     * them such that they become float32.
+     */
+    t1 = float32_mul(e1 << 16, e2 << 16, &bf_status);
+    t2 = float32_mul(e1 & 0xffff0000u, e2 & 0xffff0000u, &bf_status);
+    t1 = float32_add(t1, t2, &bf_status);
+    t1 = float32_add(sum, t1, &bf_status);
+
+    return t1;
+}
+
+void HELPER(gvec_bfdot)(void *vd, void *vn, void *vm, void *va, uint32_t desc)
+{
+    intptr_t i, opr_sz = simd_oprsz(desc);
+    float32 *d = vd, *a = va;
+    uint32_t *n = vn, *m = vm;
+
+    for (i = 0; i < opr_sz / 4; ++i) {
+        d[i] = bfdotadd(a[i], n[i], m[i]);
+    }
+    clear_tail(d, opr_sz, simd_maxsz(desc));
+}