[sw] Delete the wacky macro impl of popcnt in common.h

The one use of it wasn't necessary, and, in the future,
__builtin_popcnt() should be used, instead.

Signed-off-by: Miguel Young de la Sota <mcyoung@google.com>

sw/device/lib/common.h

diff --git a/sw/device/lib/common.h b/sw/device/lib/common.h
index f8078af..3aea0dc 100644
--- a/sw/device/lib/common.h
+++ b/sw/device/lib/common.h
@@ -29,13 +29,4 @@
 
 #define ARRAYSIZE(x) (sizeof(x) / sizeof(x[0]))
 
-/* Hamming weight */
-#define BITLENGTH_1(X) ((X) - (((X) >> 1) & 0x55555555))
-#define BITLENGTH_2(X) (((X)&0x33333333) + (((X) >> 2) & 0x33333333))
-#define BITLENGTH_3(X) (((X) + ((X) >> 4)) & 0x0f0f0f0f)
-#define BITLENGTH_4(X) ((X) + ((X) >> 8))
-#define BITLENGTH_5(X) ((X) + ((X) >> 16))
-#define BITLENGTH(X) \
-  ((BITLENGTH_5(BITLENGTH_4(BITLENGTH_3(BITLENGTH_2(BITLENGTH_1(X)))))) & 0x7f)
-
 #endif

sw/device/lib/spi_device.c

diff --git a/sw/device/lib/spi_device.c b/sw/device/lib/spi_device.c
index 04caa34..ac2adb2 100644
--- a/sw/device/lib/spi_device.c
+++ b/sw/device/lib/spi_device.c
@@ -59,11 +59,10 @@
  * Fifo pointers are in bytes
  */
 inline uint32_t calc_depth(uint32_t wptr, uint32_t rptr, uint32_t size) {
-  const uint32_t sram_szw = BITLENGTH(SPI_DEVICE_BUFFER_SIZE_BYTES - 1);
   uint32_t depth;
   uint32_t wptr_phase, rptr_phase, wptr_v, rptr_v;
-  wptr_phase = wptr >> sram_szw;
-  rptr_phase = rptr >> sram_szw;
+  wptr_phase = wptr & SPI_DEVICE_BUFFER_SIZE_BYTES;
+  rptr_phase = rptr & SPI_DEVICE_BUFFER_SIZE_BYTES;
   wptr_v = wptr & (SPI_DEVICE_BUFFER_SIZE_BYTES - 1);
   rptr_v = rptr & (SPI_DEVICE_BUFFER_SIZE_BYTES - 1);