linux-kernel - 答复: [????] Re: [PATCH v3 next 09/10] lib: mul_u64_u64_div

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Message-ID: <08a4b591e9ee41ca8cec888772a0fc43@baidu.com>
Date: Thu, 10 Jul 2025 09:39:51 +0000
From: "Li,Rongqing" <lirongqing@...du.com>
To: David Laight <david.laight.linux@...il.com>, Andrew Morton
	<akpm@...ux-foundation.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: "u.kleine-koenig@...libre.com" <u.kleine-koenig@...libre.com>, "Nicolas
 Pitre" <npitre@...libre.com>, Oleg Nesterov <oleg@...hat.com>, Peter Zijlstra
	<peterz@...radead.org>, Biju Das <biju.das.jz@...renesas.com>,
	"rostedt@...dmis.org" <rostedt@...dmis.org>
Subject: 答复: [????] Re: [PATCH v3 next 09/10] lib: mul_u64_u64_div_u64() Optimise the divide code

> $ cc -O2 -o div_perf div_perf.c -DMULDIV_OPT=0xc3  && sudo ./div_perf
> 0: ok   162   134    78    78    78    78    78    80    80    80
> mul_u64_u64_div_u64_new b*7/3 = 19
> 1: ok    91    91    91    91    91    91    91    91    91    91
> mul_u64_u64_div_u64_new ffff0000*ffff0000/f = 1110eeef00000000
> 2: ok    75    77    75    77    77    77    77    77    77    77
> mul_u64_u64_div_u64_new ffffffff*ffffffff/1 = fffffffe00000001
> 3: ok    89    91    91    91    91    91    89    90    91    91
> mul_u64_u64_div_u64_new ffffffff*ffffffff/2 = 7fffffff00000000
> 4: ok   147   147   128   128   128   128   128   128   128   128
> mul_u64_u64_div_u64_new 1ffffffff*ffffffff/2 = fffffffe80000000
> 5: ok   128   128   128   128   128   128   128   128   128   128
> mul_u64_u64_div_u64_new 1ffffffff*ffffffff/3 = aaaaaaa9aaaaaaab
> 6: ok   121   121   121   121   121   121   121   121   121   121
> mul_u64_u64_div_u64_new 1ffffffff*1ffffffff/4 = ffffffff00000000
> 7: ok   274   234   146   138   138   138   138   138   138   138
> mul_u64_u64_div_u64_new
> ffff000000000000*ffff000000000000/ffff000000000001 = fffeffffffffffff
> 8: ok   177   148   148   149   149   149   149   149   149   149
> mul_u64_u64_div_u64_new
> 3333333333333333*3333333333333333/5555555555555555 =
> 1eb851eb851eb851
> 9: ok   138    90   118    91    91    91    91    92    92    92
> mul_u64_u64_div_u64_new 7fffffffffffffff*2/3 = 5555555555555554
> 10: ok   113   114    86    86    84    86    86    84    87
> 87 mul_u64_u64_div_u64_new ffffffffffffffff*2/8000000000000000 = 3
> 11: ok    87    88    88    86    88    88    88    88    90
> 90 mul_u64_u64_div_u64_new ffffffffffffffff*2/c000000000000000 = 2
> 12: ok    82    86    84    86    83    86    83    86    83
> 87 mul_u64_u64_div_u64_new
> ffffffffffffffff*4000000000000004/8000000000000000 = 8000000000000007
> 13: ok    82    86    84    86    83    86    83    86    83
> 86 mul_u64_u64_div_u64_new
> ffffffffffffffff*4000000000000001/8000000000000000 = 8000000000000001
> 14: ok   189   187   138   132   132   132   131   131   131
> 131 mul_u64_u64_div_u64_new ffffffffffffffff*8000000000000001/ffffffffffffffff =
> 8000000000000001
> 15: ok   221   175   159   131   131   131   131   131   131
> 131 mul_u64_u64_div_u64_new fffffffffffffffe*8000000000000001/ffffffffffffffff
> = 8000000000000000
> 16: ok   134   132   134   134   134   135   134   134   134
> 134 mul_u64_u64_div_u64_new ffffffffffffffff*8000000000000001/fffffffffffffffe
> = 8000000000000001
> 17: ok   172   134   137   134   134   134   134   134   134
> 134 mul_u64_u64_div_u64_new ffffffffffffffff*8000000000000001/fffffffffffffffd
> = 8000000000000002
> 18: ok   182   182   129   129   129   129   129   129   129
> 129 mul_u64_u64_div_u64_new 7fffffffffffffff*ffffffffffffffff/c000000000000000
> = aaaaaaaaaaaaaaa8
> 19: ok   130   129   130   129   129   129   129   129   129
> 129 mul_u64_u64_div_u64_new ffffffffffffffff*7fffffffffffffff/a000000000000000
> = ccccccccccccccca
> 20: ok   130   129   129   129   129   129   129   129   129
> 129 mul_u64_u64_div_u64_new ffffffffffffffff*7fffffffffffffff/9000000000000000
> = e38e38e38e38e38b
> 21: ok   130   129   129   129   129   129   129   129   129
> 129 mul_u64_u64_div_u64_new 7fffffffffffffff*7fffffffffffffff/5000000000000000
> = ccccccccccccccc9
> 22: ok   206   140   138   138   138   138   138   138   138
> 138 mul_u64_u64_div_u64_new ffffffffffffffff*fffffffffffffffe/ffffffffffffffff =
> fffffffffffffffe
> 23: ok   174   140   138   138   138   138   138   138   138
> 138 mul_u64_u64_div_u64_new
> e6102d256d7ea3ae*70a77d0be4c31201/d63ec35ab3220357 =
> 78f8bf8cc86c6e18
> 24: ok   135   137   137   137   137   137   137   137   137
> 137 mul_u64_u64_div_u64_new
> f53bae05cb86c6e1*3847b32d2f8d32e0/cfd4f55a647f403c =
> 42687f79d8998d35
> 25: ok   134   136   136   136   136   136   136   136   136
> 136 mul_u64_u64_div_u64_new
> 9951c5498f941092*1f8c8bfdf287a251/a3c8dc5f81ea3fe2 = 1d887cb25900091f
> 26: ok   136   134   134   134   134   134   134   134   134
> 134 mul_u64_u64_div_u64_new
> 374fee9daa1bb2bb*d0bfbff7b8ae3ef/c169337bd42d5179 = 3bb2dbaffcbb961
> 27: ok   139   138   138   138   138   138   138   138   138
> 138 mul_u64_u64_div_u64_new
> eac0d03ac10eeaf0*89be05dfa162ed9b/92bb1679a41f0e4b =
> dc5f5cc9e270d216
> 28: ok   130   143    95    95    96    96    96    96    96
> 96 mul_u64_u64_div_u64_new
> 2d256d7ea3ae*7d0be4c31201/d63ec35ab3220357 = 1a599d6e
> 29: ok   169   158   158   138   138   138   138   138   138
> 138 mul_u64_u64_div_u64_new
> eac0d03ac10eeaf0*89be05dfa162ed9b/92bb1679a41f0e4b =
> dc5f5cc9e270d216
> 30: ok   178   164   144   147   147   147   147   147   147
> 147 mul_u64_u64_div_u64_new
> 2d256d7ea3ae*7d0be4c31201/63ec35ab3220357 = 387f55cef
> 31: ok   163   128   128   128   128   128   128   128   128
> 128 mul_u64_u64_div_u64_new
> eac0d03ac10eeaf0*89be05dfa162ed9b/92bb000000000000 =
> dc5f7e8b334db07d
> 32: ok   163   184   137   136   136   138   138   138   138
> 138 mul_u64_u64_div_u64_new
> eac0d03ac10eeaf0*89be05dfa162ed9b/92bb1679a41f0e4b =
> dc5f5cc9e270d216
> 

Nice work!

Is it necessary to add an exception test case, such as a case for division result overflowing 64bit?

Thanks

-Li