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torvalds
GitHub Repository: torvalds/linux
 Path: blob/master/arch/mips/lib/multi3.c
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// SPDX-License-Identifier: GPL-2.0

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#include <linux/export.h>

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#include "libgcc.h"

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/*

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 * GCC 7 & older can suboptimally generate __multi3 calls for mips64r6, so for

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 * that specific case only we implement that intrinsic here.

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 *

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 * See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82981

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 */

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#if defined(CONFIG_64BIT) && defined(CONFIG_CPU_MIPSR6) && (__GNUC__ < 8)

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/* multiply 64-bit values, low 64-bits returned */

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static inline long long notrace dmulu(long long a, long long b)

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{

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	long long res;

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	asm ("dmulu %0,%1,%2" : "=r" (res) : "r" (a), "r" (b));

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	return res;

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}

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/* multiply 64-bit unsigned values, high 64-bits of 128-bit result returned */

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static inline long long notrace dmuhu(long long a, long long b)

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{

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	long long res;

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	asm ("dmuhu %0,%1,%2" : "=r" (res) : "r" (a), "r" (b));

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	return res;

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}

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/* multiply 128-bit values, low 128-bits returned */

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ti_type notrace __multi3(ti_type a, ti_type b)

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{

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	TWunion res, aa, bb;

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	aa.ti = a;

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	bb.ti = b;

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	/*

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	 * a * b =           (a.lo * b.lo)

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	 *         + 2^64  * (a.hi * b.lo + a.lo * b.hi)

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	 *        [+ 2^128 * (a.hi * b.hi)]

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	 */

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	res.s.low = dmulu(aa.s.low, bb.s.low);

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	res.s.high = dmuhu(aa.s.low, bb.s.low);

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	res.s.high += dmulu(aa.s.high, bb.s.low);

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	res.s.high += dmulu(aa.s.low, bb.s.high);

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	return res.ti;

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}

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EXPORT_SYMBOL(__multi3);

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#endif /* 64BIT && CPU_MIPSR6 && GCC7 */

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