[dpdk-dev] [PATCH] common: introduce an integer log2 function

[Olivier Matz]

At some places, the log2() function is used despite this function
works on float. This introduces a dependency to the math lib but
most of the time it is not required because we want an integer log2.

Add a new helper to do this job and fix 2 drivers.

Signed-off-by: Olivier Matz <olivier.matz at 6wind.com>
---
 drivers/net/nfp/nfp_net.c                  |  6 ++----
 lib/librte_eal/common/include/rte_common.h | 17 +++++++++++++++++
 mk/rte.app.mk                              |  2 +-
 3 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/drivers/net/nfp/nfp_net.c b/drivers/net/nfp/nfp_net.c
index a1ad97ad5..0e6a729ef 100644
--- a/drivers/net/nfp/nfp_net.c
+++ b/drivers/net/nfp/nfp_net.c
@@ -39,8 +39,6 @@
  * Netronome vNIC DPDK Poll-Mode Driver: Main entry point
  */
 
-#include <math.h>
-
 #include <rte_byteorder.h>
 #include <rte_common.h>
 #include <rte_log.h>
@@ -1493,7 +1491,7 @@ nfp_net_rx_queue_setup(struct rte_eth_dev *dev,
 	 * of descriptors in log2 format
 	 */
 	nn_cfg_writeq(hw, NFP_NET_CFG_RXR_ADDR(queue_idx), rxq->dma);
-	nn_cfg_writeb(hw, NFP_NET_CFG_RXR_SZ(queue_idx), log2(nb_desc));
+	nn_cfg_writeb(hw, NFP_NET_CFG_RXR_SZ(queue_idx), rte_log2_u32(nb_desc));
 
 	return 0;
 }
@@ -1647,7 +1645,7 @@ nfp_net_tx_queue_setup(struct rte_eth_dev *dev, uint16_t queue_idx,
 	 * of descriptors in log2 format
 	 */
 	nn_cfg_writeq(hw, NFP_NET_CFG_TXR_ADDR(queue_idx), txq->dma);
-	nn_cfg_writeb(hw, NFP_NET_CFG_TXR_SZ(queue_idx), log2(nb_desc));
+	nn_cfg_writeb(hw, NFP_NET_CFG_TXR_SZ(queue_idx), rte_log2_u32(nb_desc));
 
 	return 0;
 }
diff --git a/lib/librte_eal/common/include/rte_common.h b/lib/librte_eal/common/include/rte_common.h
index e057f6e21..eea0054c1 100644
--- a/lib/librte_eal/common/include/rte_common.h
+++ b/lib/librte_eal/common/include/rte_common.h
@@ -326,6 +326,23 @@ rte_bsf32(uint32_t v)
 	return __builtin_ctz(v);
 }
 
+/**
+ * Return the rounded-up log2 of a integer.
+ *
+ * @param v
+ *     The input parameter.
+ * @return
+ *     The rounded-up log2 of the input, or 0 if the input is 0.
+ */
+static inline uint32_t
+rte_log2_u32(uint32_t v)
+{
+	if (v == 0)
+		return 0;
+	v = rte_align32pow2(v);
+	return rte_bsf32(v);
+}
+
 #ifndef offsetof
 /** Return the offset of a field in a structure. */
 #define offsetof(TYPE, MEMBER)  __builtin_offsetof (TYPE, MEMBER)
diff --git a/mk/rte.app.mk b/mk/rte.app.mk
index 4c659e971..2fcd388e6 100644
--- a/mk/rte.app.mk
+++ b/mk/rte.app.mk
@@ -125,7 +125,7 @@ endif
 _LDLIBS-$(CONFIG_RTE_LIBRTE_LIO_PMD)        += -lrte_pmd_lio
 _LDLIBS-$(CONFIG_RTE_LIBRTE_MLX4_PMD)       += -lrte_pmd_mlx4 -libverbs
 _LDLIBS-$(CONFIG_RTE_LIBRTE_MLX5_PMD)       += -lrte_pmd_mlx5 -libverbs
-_LDLIBS-$(CONFIG_RTE_LIBRTE_NFP_PMD)        += -lrte_pmd_nfp -lm
+_LDLIBS-$(CONFIG_RTE_LIBRTE_NFP_PMD)        += -lrte_pmd_nfp
 _LDLIBS-$(CONFIG_RTE_LIBRTE_PMD_NULL)       += -lrte_pmd_null
 _LDLIBS-$(CONFIG_RTE_LIBRTE_PMD_PCAP)       += -lrte_pmd_pcap -lpcap
 _LDLIBS-$(CONFIG_RTE_LIBRTE_QEDE_PMD)       += -lrte_pmd_qede
-- 
2.11.0