[PATCH v2 3/6] raid6 algorithms: xor_syndrome() for generic int

[Markus Stockhausen <stockhausen@xxxxxxxxxxx>]

commit 792ad6dd60e0e45f240d1a6e9cdad6bd45be6d46
Author: Markus Stockhausen <markus.stockhausen@xxxxxxxxxxx>
Date:   Tue Aug 19 16:00:57 2014 +0000

    raid6 algorithms: xor_syndrome() for generic int
    
    v2: xor_syndrome() with function header
    
    Start the algorithms with the very basic one. It is left and right
    optimized. That means we can avoid all calculations for unneeded pages
    above the right stop offset. For pages below the left start offset we
    still need the syndrome multiplication but without reading data pages.

diff --git a/lib/raid6/int.uc b/lib/raid6/int.uc
index 5ca60be..558aeac 100644
--- a/lib/raid6/int.uc
+++ b/lib/raid6/int.uc
@@ -107,9 +107,47 @@ static void raid6_int$#_gen_syndrome(int disks, size_t bytes, void **ptrs)
 	}
 }
 
+static void raid6_int$#_xor_syndrome(int disks, int start, int stop,
+				     size_t bytes, void **ptrs)
+{
+	u8 **dptr = (u8 **)ptrs;
+	u8 *p, *q;
+	int d, z, z0;
+
+	unative_t wd$$, wq$$, wp$$, w1$$, w2$$;
+
+	z0 = stop;		/* P/Q right side optimization */
+	p = dptr[disks-2];	/* XOR parity */
+	q = dptr[disks-1];	/* RS syndrome */
+
+	for ( d = 0 ; d < bytes ; d += NSIZE*$# ) {
+		/* P/Q data pages */
+		wq$$ = wp$$ = *(unative_t *)&dptr[z0][d+$$*NSIZE];
+		for ( z = z0-1 ; z >= start ; z-- ) {
+			wd$$ = *(unative_t *)&dptr[z][d+$$*NSIZE];
+			wp$$ ^= wd$$;
+			w2$$ = MASK(wq$$);
+			w1$$ = SHLBYTE(wq$$);
+			w2$$ &= NBYTES(0x1d);
+			w1$$ ^= w2$$;
+			wq$$ = w1$$ ^ wd$$;
+		}
+		/* P/Q left side optimization */
+		for ( z = start-1 ; z >= 0 ; z-- ) {
+			w2$$ = MASK(wq$$);
+			w1$$ = SHLBYTE(wq$$);
+			w2$$ &= NBYTES(0x1d);
+			wq$$ = w1$$ ^ w2$$;
+		}
+		*(unative_t *)&p[d+NSIZE*$$] ^= wp$$;
+		*(unative_t *)&q[d+NSIZE*$$] ^= wq$$;
+	}
+
+}
+
 const struct raid6_calls raid6_intx$# = {
 	raid6_int$#_gen_syndrome,
-	NULL,			/* XOR not yet implemented */
+	raid6_int$#_xor_syndrome,
 	NULL,			/* always valid */
 	"int" NSTRING "x$#",
 	0

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