arch/mips/lib/multi3.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/export.h>
   3
   4 #include "libgcc.h"
   5
   6 /*
   7  * GCC 7 suboptimally generates __multi3 calls for mips64r6, so for that
   8  * specific case only we'll implement it here.
   9  *
  10  * See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82981
  11  */
  12 #if defined(CONFIG_64BIT) && defined(CONFIG_CPU_MIPSR6) && (__GNUC__ == 7)
  13
  14 /* multiply 64-bit values, low 64-bits returned */
  15 static inline long long notrace dmulu(long long a, long long b)
  16 {
  17         long long res;
  18
  19         asm ("dmulu %0,%1,%2" : "=r" (res) : "r" (a), "r" (b));
  20         return res;
  21 }
  22
  23 /* multiply 64-bit unsigned values, high 64-bits of 128-bit result returned */
  24 static inline long long notrace dmuhu(long long a, long long b)
  25 {
  26         long long res;
  27
  28         asm ("dmuhu %0,%1,%2" : "=r" (res) : "r" (a), "r" (b));
  29         return res;
  30 }
  31
  32 /* multiply 128-bit values, low 128-bits returned */
  33 ti_type notrace __multi3(ti_type a, ti_type b)
  34 {
  35         TWunion res, aa, bb;
  36
  37         aa.ti = a;
  38         bb.ti = b;
  39
  40         /*
  41          * a * b =           (a.lo * b.lo)
  42          *         + 2^64  * (a.hi * b.lo + a.lo * b.hi)
  43          *        [+ 2^128 * (a.hi * b.hi)]
  44          */
  45         res.s.low = dmulu(aa.s.low, bb.s.low);
  46         res.s.high = dmuhu(aa.s.low, bb.s.low);
  47         res.s.high += dmulu(aa.s.high, bb.s.low);
  48         res.s.high += dmulu(aa.s.low, bb.s.high);
  49
  50         return res.ti;
  51 }
  52 EXPORT_SYMBOL(__multi3);
  53
  54 #endif /* 64BIT && CPU_MIPSR6 && GCC7 */