[Qemu-devel] [PATCH v3 5/9] Convert ffs() != 0 callers to ctz32()

[Stefan Hajnoczi <stefanha@redhat.com>]

There are a number of ffs(3) callers that do roughly:

  bit = ffs(val);
  if (bit) {
      do_something(bit - 1);
  }

This pattern can be converted to ctz32() like this:

  zeroes = ctz32(val);
  if (zeroes != 32) {
      do_something(zeroes);
  }

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 hw/arm/omap1.c              |  6 ++----
 hw/char/virtio-serial-bus.c |  8 ++++----
 hw/gpio/omap_gpio.c         | 13 +++++--------
 hw/i2c/omap_i2c.c           | 10 +++++++---
 hw/intc/allwinner-a10-pic.c |  8 ++++----
 kvm-all.c                   |  8 ++++----
 6 files changed, 26 insertions(+), 27 deletions(-)

diff --git a/hw/arm/omap1.c b/hw/arm/omap1.c
index 0615044..4c08fa0 100644
--- a/hw/arm/omap1.c
+++ b/hw/arm/omap1.c
@@ -2002,8 +2002,7 @@ static void omap_mpuio_write(void *opaque, hwaddr addr,
     case 0x04:	/* OUTPUT_REG */
         diff = (s->outputs ^ value) & ~s->dir;
         s->outputs = value;
-        while ((ln = ffs(diff))) {
-            ln --;
+        while ((ln = ctz32(diff)) != 32) {
             if (s->handler[ln])
                 qemu_set_irq(s->handler[ln], (value >> ln) & 1);
             diff &= ~(1 << ln);
@@ -2015,8 +2014,7 @@ static void omap_mpuio_write(void *opaque, hwaddr addr,
         s->dir = value;
 
         value = s->outputs & ~s->dir;
-        while ((ln = ffs(diff))) {
-            ln --;
+        while ((ln = ctz32(diff)) != 32) {
             if (s->handler[ln])
                 qemu_set_irq(s->handler[ln], (value >> ln) & 1);
             diff &= ~(1 << ln);
diff --git a/hw/char/virtio-serial-bus.c b/hw/char/virtio-serial-bus.c
index d14e872..02a692c 100644
--- a/hw/char/virtio-serial-bus.c
+++ b/hw/char/virtio-serial-bus.c
@@ -814,12 +814,12 @@ static uint32_t find_free_port_id(VirtIOSerial *vser)
 
     max_nr_ports = vser->serial.max_virtserial_ports;
     for (i = 0; i < (max_nr_ports + 31) / 32; i++) {
-        uint32_t map, bit;
+        uint32_t map, zeroes;
 
         map = vser->ports_map[i];
-        bit = ffs(~map);
-        if (bit) {
-            return (bit - 1) + i * 32;
+        zeroes = ctz32(~map);
+        if (zeroes != 32) {
+            return zeroes + i * 32;
         }
     }
     return VIRTIO_CONSOLE_BAD_ID;
diff --git a/hw/gpio/omap_gpio.c b/hw/gpio/omap_gpio.c
index 9a43486..d92f8cf 100644
--- a/hw/gpio/omap_gpio.c
+++ b/hw/gpio/omap_gpio.c
@@ -125,8 +125,7 @@ static void omap_gpio_write(void *opaque, hwaddr addr,
     case 0x04:	/* DATA_OUTPUT */
         diff = (s->outputs ^ value) & ~s->dir;
         s->outputs = value;
-        while ((ln = ffs(diff))) {
-            ln --;
+        while ((ln = ctz32(diff)) != 32) {
             if (s->handler[ln])
                 qemu_set_irq(s->handler[ln], (value >> ln) & 1);
             diff &= ~(1 << ln);
@@ -138,8 +137,7 @@ static void omap_gpio_write(void *opaque, hwaddr addr,
         s->dir = value;
 
         value = s->outputs & ~s->dir;
-        while ((ln = ffs(diff))) {
-            ln --;
+        while ((ln = ctz32(diff)) != 32) {
             if (s->handler[ln])
                 qemu_set_irq(s->handler[ln], (value >> ln) & 1);
             diff &= ~(1 << ln);
@@ -253,8 +251,7 @@ static inline void omap2_gpio_module_out_update(struct omap2_gpio_s *s,
 
     s->outputs ^= diff;
     diff &= ~s->dir;
-    while ((ln = ffs(diff))) {
-        ln --;
+    while ((ln = ctz32(diff)) != 32) {
         qemu_set_irq(s->handler[ln], (s->outputs >> ln) & 1);
         diff &= ~(1 << ln);
     }
@@ -442,8 +439,8 @@ static void omap2_gpio_module_write(void *opaque, hwaddr addr,
         s->dir = value;
 
         value = s->outputs & ~s->dir;
-        while ((ln = ffs(diff))) {
-            diff &= ~(1 <<-- ln);
+        while ((ln = ctz32(diff)) != 32) {
+            diff &= ~(1 << ln);
             qemu_set_irq(s->handler[ln], (value >> ln) & 1);
         }
 
diff --git a/hw/i2c/omap_i2c.c b/hw/i2c/omap_i2c.c
index d63278d..b6f544a 100644
--- a/hw/i2c/omap_i2c.c
+++ b/hw/i2c/omap_i2c.c
@@ -171,9 +171,13 @@ static uint32_t omap_i2c_read(void *opaque, hwaddr addr)
     case 0x0c:	/* I2C_IV */
         if (s->revision >= OMAP2_INTR_REV)
             break;
-        ret = ffs(s->stat & s->mask);
-        if (ret)
-            s->stat ^= 1 << (ret - 1);
+        ret = ctz32(s->stat & s->mask);
+        if (ret != 32) {
+            s->stat ^= 1 << ret;
+            ret++;
+        } else {
+            ret = 0;
+        }
         omap_i2c_interrupts_update(s);
         return ret;
 
diff --git a/hw/intc/allwinner-a10-pic.c b/hw/intc/allwinner-a10-pic.c
index de820b9..eed7621 100644
--- a/hw/intc/allwinner-a10-pic.c
+++ b/hw/intc/allwinner-a10-pic.c
@@ -23,7 +23,7 @@
 static void aw_a10_pic_update(AwA10PICState *s)
 {
     uint8_t i;
-    int irq = 0, fiq = 0, pending;
+    int irq = 0, fiq = 0, zeroes;
 
     s->vector = 0;
 
@@ -32,9 +32,9 @@ static void aw_a10_pic_update(AwA10PICState *s)
         fiq |= s->select[i] & s->irq_pending[i] & ~s->mask[i];
 
         if (!s->vector) {
-            pending = ffs(s->irq_pending[i] & ~s->mask[i]);
-            if (pending) {
-                s->vector = (i * 32 + pending - 1) * 4;
+            zeroes = ctz32(s->irq_pending[i] & ~s->mask[i]);
+            if (zeroes != 32) {
+                s->vector = (i * 32 + zeroes) * 4;
             }
         }
     }
diff --git a/kvm-all.c b/kvm-all.c
index 335438a..ae0208d 100644
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -1141,18 +1141,18 @@ static int kvm_irqchip_get_virq(KVMState *s)
 {
     uint32_t *word = s->used_gsi_bitmap;
     int max_words = ALIGN(s->gsi_count, 32) / 32;
-    int i, bit;
+    int i, zeroes;
     bool retry = true;
 
 again:
     /* Return the lowest unused GSI in the bitmap */
     for (i = 0; i < max_words; i++) {
-        bit = ffs(~word[i]);
-        if (!bit) {
+        zeroes = ctz32(~word[i]);
+        if (zeroes == 32) {
             continue;
         }
 
-        return bit - 1 + i * 32;
+        return zeroes + i * 32;
     }
     if (!s->direct_msi && retry) {
         retry = false;
-- 
2.1.0