Integrated RandomX, added RandomXL (Loki)

src/crypto/randomx/reciprocal.c

@@ -0,0 +1,80 @@
+/*
+Copyright (c) 2018-2019, tevador <tevador@gmail.com>
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+	* Redistributions of source code must retain the above copyright
+	  notice, this list of conditions and the following disclaimer.
+	* 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.
+	* Neither the name of the copyright holder nor the
+	  names of its contributors may be used to endorse or promote products
+	  derived from this software without specific prior written permission.
+
+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 HOLDER 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.
+*/
+
+#include <assert.h>
+#include "reciprocal.h"
+
+/*
+	Calculates rcp = 2**x / divisor for highest integer x such that rcp < 2**64.
+	divisor must not be 0 or a power of 2
+
+	Equivalent x86 assembly (divisor in rcx):
+
+	mov edx, 1
+	mov r8, rcx
+	xor eax, eax
+	bsr rcx, rcx
+	shl rdx, cl
+	div r8
+	ret
+
+*/
+uint64_t randomx_reciprocal(uint64_t divisor) {
+
+	assert(divisor != 0);
+
+	const uint64_t p2exp63 = 1ULL << 63;
+
+	uint64_t quotient = p2exp63 / divisor, remainder = p2exp63 % divisor;
+
+	unsigned bsr = 0; //highest set bit in divisor
+
+	for (uint64_t bit = divisor; bit > 0; bit >>= 1)
+		bsr++;
+
+	for (unsigned shift = 0; shift < bsr; shift++) {
+		if (remainder >= divisor - remainder) {
+			quotient = quotient * 2 + 1;
+			remainder = remainder * 2 - divisor;
+		}
+		else {
+			quotient = quotient * 2;
+			remainder = remainder * 2;
+		}
+	}
+
+	return quotient;
+}
+
+#if !RANDOMX_HAVE_FAST_RECIPROCAL
+
+uint64_t randomx_reciprocal_fast(uint64_t divisor) {
+	return randomx_reciprocal(divisor);
+}
+
+#endif