coldboot: add lfsr.h by Anton Blanchard

diff --git a/coldboot/lfsr.h b/coldboot/lfsr.h
new file mode 100644 (file)
index 0000000..8326b81
--- /dev/null
+++ b/coldboot/lfsr.h
@@ -0,0 +1,109 @@
+#include <limits.h>
+
+/*
+ * Copyright (C) 2020, Anton Blanchard <anton@linux.ibm.com>, IBM
+ *
+ * Redistribution and use in source and binary forms, with or without modification,
+ * are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+ * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/*
+ * Galois LFSR
+ *
+ * Polynomials verified with https://bitbucket.org/gallen/mlpolygen/
+ */
+static inline unsigned long lfsr(unsigned long bits, unsigned long prev)
+{
+       static const unsigned long lfsr_taps[] = {
+               0x0,
+               0x0,
+               0x3,
+               0x6,
+               0xc,
+               0x14,
+               0x30,
+               0x60,
+               0xb8,
+               0x110,
+               0x240,
+               0x500,
+               0x829,
+               0x100d,
+               0x2015,
+               0x6000,
+               0xd008,
+               0x12000,
+               0x20400,
+               0x40023,
+               0x90000,
+               0x140000,
+               0x300000,
+               0x420000,
+               0xe10000,
+               0x1200000,
+               0x2000023,
+               0x4000013,
+               0x9000000,
+               0x14000000,
+               0x20000029,
+               0x48000000,
+               0x80200003,
+#ifdef __LP64__
+               0x100080000,
+               0x204000003,
+               0x500000000,
+               0x801000000,
+               0x100000001f,
+               0x2000000031,
+               0x4400000000,
+               0xa000140000,
+               0x12000000000,
+               0x300000c0000,
+               0x63000000000,
+               0xc0000030000,
+               0x1b0000000000,
+               0x300003000000,
+               0x420000000000,
+               0xc00000180000,
+               0x1008000000000,
+               0x3000000c00000,
+               0x6000c00000000,
+               0x9000000000000,
+               0x18003000000000,
+               0x30000000030000,
+               0x40000040000000,
+               0xc0000600000000,
+               0x102000000000000,
+               0x200004000000000,
+               0x600003000000000,
+               0xc00000000000000,
+               0x1800300000000000,
+               0x3000000000000030,
+               0x6000000000000000,
+               0x800000000000000d
+#endif
+       };
+       unsigned long lsb = prev & 1;
+
+       prev >>= 1;
+       prev ^= (-lsb) & lfsr_taps[bits];
+
+       return prev;
+}