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libsec: avoid temp variables in chacha/salsa ENCRYPT() macro

given that we only pass uchar* with constant offsets
to the s and d arguments of ENCRYPT(), we do not need
the temporary variables sp/dp and the compiler is
smart enougth to combine the const offset with the ones
from GET4() and PUT4() and emit single load and store
instructions for the byte accesses.

--- a/sys/src/libsec/port/chacha.c

+++ b/sys/src/libsec/port/chacha.c

@@ -32,12 +32,9 @@

 #define ENCRYPT(s, x, y, d) {\

 	u32int v; \

-	uchar *sp, *dp; \

-	sp = (s); \

-	v = GET4(sp); \

+	v = GET4(s); \

 	v ^= (x)+(y); \

-	dp = (d); \

-	PUT4(dp, v); \

+	PUT4(d, v); \

 }

 static uchar sigma[16] = "expand 32-byte k";

--- a/sys/src/libsec/port/salsa.c

+++ b/sys/src/libsec/port/salsa.c

@@ -9,12 +9,9 @@

 #define ENCRYPT(s, x, y, d) {\

 	u32int v; \

-	uchar *sp, *dp; \

-	sp = (s); \

-	v = GET4(sp); \

+	v = GET4(s); \

 	v ^= (x)+(y); \

-	dp = (d); \

-	PUT4(dp, v); \

+	PUT4(d, v); \

 }

 static uchar sigma[16] = "expand 32-byte k";