kernel / pub / scm / linux / kernel / git / vireshk / linux / a497c3ba1d97fc69c1e78e7b96435ba8c2cb42ee / . / arch / alpha / lib / ev6-csum_ipv6_magic.S

/* | |

* arch/alpha/lib/ev6-csum_ipv6_magic.S | |

* 21264 version contributed by Rick Gorton <rick.gorton@alpha-processor.com> | |

* | |

* unsigned short csum_ipv6_magic(struct in6_addr *saddr, | |

* struct in6_addr *daddr, | |

* __u32 len, | |

* unsigned short proto, | |

* unsigned int csum); | |

* | |

* Much of the information about 21264 scheduling/coding comes from: | |

* Compiler Writer's Guide for the Alpha 21264 | |

* abbreviated as 'CWG' in other comments here | |

* ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html | |

* Scheduling notation: | |

* E - either cluster | |

* U - upper subcluster; U0 - subcluster U0; U1 - subcluster U1 | |

* L - lower subcluster; L0 - subcluster L0; L1 - subcluster L1 | |

* Try not to change the actual algorithm if possible for consistency. | |

* Determining actual stalls (other than slotting) doesn't appear to be easy to do. | |

* | |

* unsigned short csum_ipv6_magic(struct in6_addr *saddr, | |

* struct in6_addr *daddr, | |

* __u32 len, | |

* unsigned short proto, | |

* unsigned int csum); | |

* | |

* Swap <proto> (takes form 0xaabb) | |

* Then shift it left by 48, so result is: | |

* 0xbbaa0000 00000000 | |

* Then turn it back into a sign extended 32-bit item | |

* 0xbbaa0000 | |

* | |

* Swap <len> (an unsigned int) using Mike Burrows' 7-instruction sequence | |

* (we can't hide the 3-cycle latency of the unpkbw in the 6-instruction sequence) | |

* Assume input takes form 0xAABBCCDD | |

* | |

* Finally, original 'folding' approach is to split the long into 4 unsigned shorts | |

* add 4 ushorts, resulting in ushort/carry | |

* add carry bits + ushort --> ushort | |

* add carry bits + ushort --> ushort (in case the carry results in an overflow) | |

* Truncate to a ushort. (took 13 instructions) | |

* From doing some testing, using the approach in checksum.c:from64to16() | |

* results in the same outcome: | |

* split into 2 uints, add those, generating a ulong | |

* add the 3 low ushorts together, generating a uint | |

* a final add of the 2 lower ushorts | |

* truncating the result. | |

* | |

* Misalignment handling added by Ivan Kokshaysky <ink@jurassic.park.msu.ru> | |

* The cost is 16 instructions (~8 cycles), including two extra loads which | |

* may cause additional delay in rare cases (load-load replay traps). | |

*/ | |

.globl csum_ipv6_magic | |

.align 4 | |

.ent csum_ipv6_magic | |

.frame $30,0,$26,0 | |

csum_ipv6_magic: | |

.prologue 0 | |

ldq_u $0,0($16) # L : Latency: 3 | |

inslh $18,7,$4 # U : 0000000000AABBCC | |

ldq_u $1,8($16) # L : Latency: 3 | |

sll $19,8,$7 # U : U L U L : 0x00000000 00aabb00 | |

and $16,7,$6 # E : src misalignment | |

ldq_u $5,15($16) # L : Latency: 3 | |

zapnot $20,15,$20 # U : zero extend incoming csum | |

ldq_u $2,0($17) # L : U L U L : Latency: 3 | |

extql $0,$6,$0 # U : | |

extqh $1,$6,$22 # U : | |

ldq_u $3,8($17) # L : Latency: 3 | |

sll $19,24,$19 # U : U U L U : 0x000000aa bb000000 | |

cmoveq $6,$31,$22 # E : src aligned? | |

ldq_u $23,15($17) # L : Latency: 3 | |

inswl $18,3,$18 # U : 000000CCDD000000 | |

addl $19,$7,$19 # E : U L U L : <sign bits>bbaabb00 | |

or $0,$22,$0 # E : 1st src word complete | |

extql $1,$6,$1 # U : | |

or $18,$4,$18 # E : 000000CCDDAABBCC | |

extqh $5,$6,$5 # U : L U L U | |

and $17,7,$6 # E : dst misalignment | |

extql $2,$6,$2 # U : | |

or $1,$5,$1 # E : 2nd src word complete | |

extqh $3,$6,$22 # U : L U L U : | |

cmoveq $6,$31,$22 # E : dst aligned? | |

extql $3,$6,$3 # U : | |

addq $20,$0,$20 # E : begin summing the words | |

extqh $23,$6,$23 # U : L U L U : | |

srl $18,16,$4 # U : 0000000000CCDDAA | |

or $2,$22,$2 # E : 1st dst word complete | |

zap $19,0x3,$19 # U : <sign bits>bbaa0000 | |

or $3,$23,$3 # E : U L U L : 2nd dst word complete | |

cmpult $20,$0,$0 # E : | |

addq $20,$1,$20 # E : | |

zapnot $18,0xa,$18 # U : 00000000DD00BB00 | |

zap $4,0xa,$4 # U : U U L L : 0000000000CC00AA | |

or $18,$4,$18 # E : 00000000DDCCBBAA | |

nop # E : | |

cmpult $20,$1,$1 # E : | |

addq $20,$2,$20 # E : U L U L | |

cmpult $20,$2,$2 # E : | |

addq $20,$3,$20 # E : | |

cmpult $20,$3,$3 # E : (1 cycle stall on $20) | |

addq $20,$18,$20 # E : U L U L (1 cycle stall on $20) | |

cmpult $20,$18,$18 # E : | |

addq $20,$19,$20 # E : (1 cycle stall on $20) | |

addq $0,$1,$0 # E : merge the carries back into the csum | |

addq $2,$3,$2 # E : | |

cmpult $20,$19,$19 # E : | |

addq $18,$19,$18 # E : (1 cycle stall on $19) | |

addq $0,$2,$0 # E : | |

addq $20,$18,$20 # E : U L U L : | |

/* (1 cycle stall on $18, 2 cycles on $20) */ | |

addq $0,$20,$0 # E : | |

zapnot $0,15,$1 # U : Start folding output (1 cycle stall on $0) | |

nop # E : | |

srl $0,32,$0 # U : U L U L : (1 cycle stall on $0) | |

addq $1,$0,$1 # E : Finished generating ulong | |

extwl $1,2,$2 # U : ushort[1] (1 cycle stall on $1) | |

zapnot $1,3,$0 # U : ushort[0] (1 cycle stall on $1) | |

extwl $1,4,$1 # U : ushort[2] (1 cycle stall on $1) | |

addq $0,$2,$0 # E | |

addq $0,$1,$3 # E : Finished generating uint | |

/* (1 cycle stall on $0) */ | |

extwl $3,2,$1 # U : ushort[1] (1 cycle stall on $3) | |

nop # E : L U L U | |

addq $1,$3,$0 # E : Final carry | |

not $0,$4 # E : complement (1 cycle stall on $0) | |

zapnot $4,3,$0 # U : clear upper garbage bits | |

/* (1 cycle stall on $4) */ | |

ret # L0 : L U L U | |

.end csum_ipv6_magic |