From f6d4fe703b0148c0ffe45eea7f9290be2ce32257 Mon Sep 17 00:00:00 2001
From: Murray Steele <murray.steele@arm.com>
Date: Thu, 26 Mar 2026 12:10:52 +0000
Subject: [PATCH] Fix incorrect cast from BF16 to FP32 in SBGEMM

This change fixes a regression in SBGEMM where C is assumed to be BF16,
and so unconditionally casts the output to FP32 resulting in incorrect
outputs when beta=1.
---
 kernel/generic/gemmkernel_2x2.c | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/kernel/generic/gemmkernel_2x2.c b/kernel/generic/gemmkernel_2x2.c
index 07da2cbc87..94dcaea5f3 100644
--- a/kernel/generic/gemmkernel_2x2.c
+++ b/kernel/generic/gemmkernel_2x2.c
@@ -30,6 +30,12 @@
 
 #include "conversion_macros.h"
 
+#ifdef BGEMM
+#define C_TO_F32 TO_F32
+#else
+#define C_TO_F32
+#endif
+
 int CNAME(BLASLONG bm,BLASLONG bn,BLASLONG bk,FLOAT alpha,IFLOAT* ba,IFLOAT* bb,FLOAT* C,BLASLONG ldc
 #ifdef TRMMKERNEL
 		,BLASLONG offset
@@ -108,13 +114,13 @@ int CNAME(BLASLONG bm,BLASLONG bn,BLASLONG bk,FLOAT alpha,IFLOAT* ba,IFLOAT* bb,
                   ptrbb = ptrbb+2;
                }
              res0 = res0*ALPHA;
-             C0[0] = TO_OUTPUT(TO_F32(C0[0])+res0);
+             C0[0] = TO_OUTPUT(C_TO_F32(C0[0])+res0);
              res1 = res1*ALPHA;
-             C0[1] = TO_OUTPUT(TO_F32(C0[1])+res1);
+             C0[1] = TO_OUTPUT(C_TO_F32(C0[1])+res1);
              res2 = res2*ALPHA;
-             C1[0] = TO_OUTPUT(TO_F32(C1[0])+res2);
+             C1[0] = TO_OUTPUT(C_TO_F32(C1[0])+res2);
              res3 = res3*ALPHA;
-             C1[1] = TO_OUTPUT(TO_F32(C1[1])+res3);
+             C1[1] = TO_OUTPUT(C_TO_F32(C1[1])+res3);
              C0 = C0+2;
              C1 = C1+2;
           }
@@ -134,9 +140,9 @@ int CNAME(BLASLONG bm,BLASLONG bn,BLASLONG bk,FLOAT alpha,IFLOAT* ba,IFLOAT* bb,
                   ptrbb = ptrbb+2;
                }
              res0 = res0*ALPHA;
-             C0[0] = TO_OUTPUT(TO_F32(C0[0])+res0);
+             C0[0] = TO_OUTPUT(C_TO_F32(C0[0])+res0);
              res1 = res1*ALPHA;
-             C1[0] = TO_OUTPUT(TO_F32(C1[0])+res1);
+             C1[0] = TO_OUTPUT(C_TO_F32(C1[0])+res1);
              C0 = C0+1;
              C1 = C1+1;
           }
@@ -165,9 +171,9 @@ int CNAME(BLASLONG bm,BLASLONG bn,BLASLONG bk,FLOAT alpha,IFLOAT* ba,IFLOAT* bb,
                   ptrbb = ptrbb+1;
                }
              res0 = res0*ALPHA;
-             C0[0] = TO_OUTPUT(TO_F32(C0[0])+res0);
+             C0[0] = TO_OUTPUT(C_TO_F32(C0[0])+res0);
              res1 = res1*ALPHA;
-             C0[1] = TO_OUTPUT(TO_F32(C0[1])+res1);
+             C0[1] = TO_OUTPUT(C_TO_F32(C0[1])+res1);
              C0 = C0+2;
           }
         for (i=0; i<(bm&1); i+=1)
@@ -183,7 +189,7 @@ int CNAME(BLASLONG bm,BLASLONG bn,BLASLONG bk,FLOAT alpha,IFLOAT* ba,IFLOAT* bb,
                   ptrbb = ptrbb+1;
                }
              res0 = res0*ALPHA;
-             C0[0] = TO_OUTPUT(TO_F32(C0[0])+res0);
+             C0[0] = TO_OUTPUT(C_TO_F32(C0[0])+res0);
              C0 = C0+1;
           }
         k = (bk<<0);