[Qemu-devel] [PATCH v2 3/4] qxl: refactor rounding up to a nearest power of 2

["Radim Krčmář" <rkrcmar@redhat.com>]

We already have pow2floor, mirror it and use instead of a function with
similar results (same in used domain), to clarify our intent.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
 v2: new
 
 hw/display/qxl.c      | 23 +++++------------------
 include/qemu-common.h |  3 +++
 util/cutils.c         | 14 ++++++++++++++
 3 files changed, 22 insertions(+), 18 deletions(-)

diff --git a/hw/display/qxl.c b/hw/display/qxl.c
index 92f2d5025d70..94ff52a959d4 100644
--- a/hw/display/qxl.c
+++ b/hw/display/qxl.c
@@ -300,19 +300,6 @@ void qxl_spice_reset_cursor(PCIQXLDevice *qxl)
     qxl->ssd.cursor = cursor_builtin_hidden();
 }
 
-
-static inline uint32_t msb_mask(uint32_t val)
-{
-    uint32_t mask;
-
-    do {
-        mask = ~(val - 1) & val;
-        val &= ~mask;
-    } while (mask < val);
-
-    return mask;
-}
-
 static ram_addr_t qxl_rom_size(void)
 {
     uint32_t required_rom_size = sizeof(QXLRom) + sizeof(QXLModes) +
@@ -1921,10 +1908,10 @@ static void qxl_init_ramsize(PCIQXLDevice *qxl)
         qxl->vram32_size = 4096;
         qxl->vram_size = 4096;
     }
-    qxl->vgamem_size = msb_mask(qxl->vgamem_size * 2 - 1);
-    qxl->vga.vram_size = msb_mask(qxl->vga.vram_size * 2 - 1);
-    qxl->vram32_size = msb_mask(qxl->vram32_size * 2 - 1);
-    qxl->vram_size = msb_mask(qxl->vram_size * 2 - 1);
+    qxl->vgamem_size = pow2ceil(qxl->vgamem_size);
+    qxl->vga.vram_size = pow2ceil(qxl->vga.vram_size);
+    qxl->vram32_size = pow2ceil(qxl->vram32_size);
+    qxl->vram_size = pow2ceil(qxl->vram_size);
 }
 
 static int qxl_init_common(PCIQXLDevice *qxl)
@@ -1956,7 +1943,7 @@ static int qxl_init_common(PCIQXLDevice *qxl)
         break;
     case 4: /* qxl-4 */
         pci_device_rev = QXL_REVISION_STABLE_V12;
-        io_size = msb_mask(QXL_IO_RANGE_SIZE * 2 - 1);
+        io_size = pow2ceil(QXL_IO_RANGE_SIZE);
         break;
     default:
         error_report("Invalid revision %d for qxl device (max %d)",
diff --git a/include/qemu-common.h b/include/qemu-common.h
index 644b46dcddf3..1b5cffb4033b 100644
--- a/include/qemu-common.h
+++ b/include/qemu-common.h
@@ -418,6 +418,9 @@ static inline bool is_power_of_2(uint64_t value)
 /* round down to the nearest power of 2*/
 int64_t pow2floor(int64_t value);
 
+/* round up to the nearest power of 2 (0 if overflow) */
+uint64_t pow2ceil(uint64_t value);
+
 #include "qemu/module.h"
 
 /*
diff --git a/util/cutils.c b/util/cutils.c
index dbe7412bd88c..c2250d1ba574 100644
--- a/util/cutils.c
+++ b/util/cutils.c
@@ -483,6 +483,20 @@ int64_t pow2floor(int64_t value)
     return value;
 }
 
+/* round up to the nearest power of 2 (0 if overflow) */
+uint64_t pow2ceil(uint64_t value)
+{
+    uint8_t nlz = clz64(value);
+
+    if (is_power_of_2(value)) {
+        return value;
+    }
+    if (!nlz) {
+        return 0;
+    }
+    return 1ULL << (64 - nlz);
+}
+
 /*
  * Implementation of  ULEB128 (http://en.wikipedia.org/wiki/LEB128)
  * Input is limited to 14-bit numbers
-- 
2.3.0