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kernel: more (arm) compiler friendly mul64fract()

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the arm compiler can lift long->vlong casts on multiplcation
and convert 64x64->64 multiplication into a 32x32->64 one
with optional 64 bit accumulate.
This commit is contained in:
cinap_lenrek 2016-06-26 15:13:10 +02:00
parent 5bf09937da
commit a99cf56c7d
1 changed files with 7 additions and 11 deletions
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18
sys/src/9/port/mul64fract.c
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@ -21,19 +21,15 @@
void void
mul64fract(uvlong *r, uvlong a, uvlong b) mul64fract(uvlong *r, uvlong a, uvlong b)
{ {
uvlong bh, bl; ulong bh, bl, ah, al;
uvlong ah, al;
uvlong res;
bl = b & 0xffffffffULL; bl = b;
bh = b >> 32; bh = b >> 32;
al = a & 0xffffffffULL; al = a;
ah = a >> 32; ah = a >> 32;
res = (al*bl)>>32; *r = (((uvlong)al*(uvlong)bl)>>32)
res += (al*bh); + ((uvlong)al*(uvlong)bh)
res += (ah*bl); + ((uvlong)ah*(uvlong)bl)
res += (ah*bh)<<32; + (((uvlong)ah*(uvlong)bh)<<32);
*r = res;
} }