From: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Date: Sun, 16 Feb 2014 23:27:09 +0000 (+0100)
Subject: swd: Improve parity calculation and move it to types.h
X-Git-Tag: v0.9.0-rc1~363
X-Git-Url: https://git.sur5r.net/?a=commitdiff_plain;h=36772a7ed0c31a99c721d1ea9131a8ecc56a263d;p=openocd

swd: Improve parity calculation and move it to types.h

It could be reused by SWD drivers and in other places.

Change-Id: Ieed0cf70c111a73d3a42ed59f46a0cdd177a73d5
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/1957
Tested-by: jenkins
Reviewed-by: Paul Fertser <fercerpav@gmail.com>
---

diff --git a/src/helper/types.h b/src/helper/types.h
index 210d3c3e..3f0724c3 100644
--- a/src/helper/types.h
+++ b/src/helper/types.h
@@ -270,6 +270,25 @@ static inline void buf_bswap32(uint8_t *dst, const uint8_t *src, size_t len)
 	}
 }
 
+/**
+ * Calculate the (even) parity of a 32-bit datum.
+ * @param x The datum.
+ * @return 1 if the number of set bits in x is odd, 0 if it is even.
+ */
+static inline int parity_u32(uint32_t x)
+{
+#ifdef __GNUC__
+	return __builtin_parityl(x);
+#else
+	x ^= x >> 16;
+	x ^= x >> 8;
+	x ^= x >> 4;
+	x ^= x >> 2;
+	x ^= x >> 1;
+	return x & 1;
+#endif
+}
+
 #if defined(__ECOS)
 
 /* eCos plain lacks these definition... A series of upstream patches
diff --git a/src/jtag/swd.h b/src/jtag/swd.h
index c628fa84..b75a83e3 100644
--- a/src/jtag/swd.h
+++ b/src/jtag/swd.h
@@ -32,17 +32,6 @@
 #define SWD_CMD_PARK	(0 << 7)	/* not driven by host (pull high) */
 /* followed by TRN, 3-bits of ACK, TRN */
 
-/* pbit16 holds precomputed parity bits for each nibble */
-#define pbit(parity, nibble) ((parity) << (nibble))
-
-static const uint16_t pbit16 =
-	pbit(0, 0) | pbit(1, 1) | pbit(1, 2) | pbit(0, 3)
-	| pbit(1, 4) | pbit(0, 5) | pbit(0, 6) | pbit(1, 7)
-	| pbit(1, 8) | pbit(0, 9) | pbit(0, 0xa) | pbit(1, 0xb)
-	| pbit(0, 0xc) | pbit(1, 0xd) | pbit(1, 0xe) | pbit(0, 0xf);
-
-#define nibble_parity(nibble) (pbit16 & pbit(1, (nibble)))
-
 /**
  * Construct a "cmd" byte, in lSB bit order, which swd_driver.read_reg()
  * and swd_driver.write_reg() methods will use directly.
@@ -54,7 +43,7 @@ static inline uint8_t swd_cmd(bool is_read, bool is_ap, uint8_t regnum)
 		| ((regnum & 0xc) << 1);
 
 	/* 8 cmd bits 4:1 may be set */
-	if (nibble_parity(cmd >> 1))
+	if (parity_u32(cmd))
 		cmd |= SWD_CMD_PARITY;
 
 	/* driver handles START, STOP, and TRN */