[vlc-devel] [PATCH 04/25] cpu: add CPU feature masking

[Victorien Le Couviour--Tuffet]

This is allows to temporarily mask a CPU feature.
It can for example be useful for testing a function with several
underlying SIMD implementations.

It adds vlc_CPU_mask and vlc_CPU_unmask to the core API.
---
 include/vlc_cpu.h  |  2 ++
 src/libvlccore.sym |  2 ++
 src/misc/cpu.c     | 14 +++++++++++++-
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/include/vlc_cpu.h b/include/vlc_cpu.h
index 4222eee3ac..4509cbdc77 100644
--- a/include/vlc_cpu.h
+++ b/include/vlc_cpu.h
@@ -30,6 +30,8 @@
  * Retrieves CPU capability flags.
  */
 VLC_API unsigned vlc_CPU(void);
+VLC_API void vlc_CPU_mask(unsigned cap);
+VLC_API void vlc_CPU_unmask(unsigned cap);
 
 /**
  * Computes CPU capability flags.
diff --git a/src/libvlccore.sym b/src/libvlccore.sym
index b44431d3fd..7508a06be3 100644
--- a/src/libvlccore.sym
+++ b/src/libvlccore.sym
@@ -522,6 +522,8 @@ vlc_sem_timedwait
 vlc_control_cancel
 vlc_GetCPUCount
 vlc_CPU
+vlc_CPU_mask
+vlc_CPU_unmask
 vlc_event_attach
 vlc_event_detach
 vlc_filenamecmp
diff --git a/src/misc/cpu.c b/src/misc/cpu.c
index 504492280d..08471caeec 100644
--- a/src/misc/cpu.c
+++ b/src/misc/cpu.c
@@ -257,6 +257,8 @@ out:
     return i_capabilities;
 }
 
+static uint32_t cpu_mask = 0;
+
 unsigned vlc_CPU(void)
 {
     static atomic_uint cpu_flags = ATOMIC_VAR_INIT(-1);
@@ -267,7 +269,17 @@ unsigned vlc_CPU(void)
         atomic_store_explicit(&cpu_flags, flags, memory_order_relaxed);
     }
 
-    return flags;
+    return flags & ~cpu_mask;
+}
+
+void vlc_CPU_mask(unsigned cap)
+{
+    cpu_mask |= cap;
+}
+
+void vlc_CPU_unmask(unsigned cap)
+{
+    cpu_mask &= ~cap;
 }
 
 void vlc_CPU_dump (vlc_object_t *obj)
-- 
2.24.1