|
|
// TITLE("Compute Checksum")//++//// Copyright (c) Microsoft Corporation. All rights reserved.//// Module Name://// xsum.s//// Abstract://// This module implements a function to compute the checksum of a buffer.//// Author://// John Vert (jvert) 11-Jul-1994//// Environment://// Revision History:////--
#include "ksalpha.h"
SBTTL("Compute Checksum")//++//// ULONG// tcpxsum (// IN ULONG Checksum,// IN PUSHORT Source,// IN ULONG Length// )//// Routine Description://// This function computes the checksum of the specified buffer.//// Arguments://// Checksum (a0) - Supplies the initial checksum value.//// Source (a1) - Supplies a pointer to the checksum buffer//// Length (a2) - Supplies the length of the buffer in words.//// Return Value://// The computed checksum is returned as the function value.////--
LEAF_ENTRY(tcpxsum) zap a0, 0xf0, a0 // clear high half of a0 bis a1, zero, t6 // save initial buffer address bis zero, zero, v0 // clear accumulated checksum
//// Check if the buffer is quadword aligned.//// If the buffer is not quadword aligned, then add the leading words to the// checksum.// ldq_u t0, 0(a1) // get containing quadword of first part blbc a1, 10f // check for word alignment beq a2, 65f // if zero bytes, don't do anything extbl t0, a1, t1 // get leading byte sll t1, 8, v0 // shift it to correct spot for later byte swap addq a1, 1, a1 // increment buffer to first full word subq a2, 1, a2 // decrement byte count
10: and a1, 6, t2 // check if buffer quadword aligned beq t2, 20f // if eq, quadword aligned extql t0, t2, t0 // extract bytes to checksum and a1, 7, t3 // compute bytes summed subq zero, t3, t3 addq t3, 8, t3 addq a1, 8, a1 // advance buffer address to next qword bic a1, 7, a1 // subq a2, t3, t2 blt t2, 55f // if ltz, too many, jump to residual code
addq v0, t0, v0 // add bytes to partial checksum cmpult v0, t0, t1 // generate carry addq t1, v0, v0 // add carry back into checksum
bis t2, zero, a2 // reduce count of bytes to checksum beq t2, 60f // if eq, no more bytes
20://// Compute the checksum in 64-byte blocks// bic a2, 7, t4 // subtract out residual bytes beq t4, 40f // if eq, no quadwords to checksum subq zero, t4, t2 // compute negative of byte count and t2, 15 << 2, t3 // compute bytes in first iteration ldq t0, 0(a1) // get first quadword to checksum beq t3, 35f // if eq, full 64-byte block subq a1, t3, a1 // bias buffer address by offset bic t4, 64-1, t4 // subtract out bytes in first iteration lda t2, 30f // get base address of code vector addl t3, t3, t3 // addq t3, t2, t2 // compute code vector offset bis t0, zero, t1 // copy first quadword to checksum jmp (t2) // dispatch
30://// The following code vector computes the checksum of a 64-byte block.//.set noreorder ldq t1, 8(a1) addq v0, t0, v0 cmpult v0, t0, t2 addq v0, t2, v0
ldq t0, 16(a1) addq v0, t1, v0 cmpult v0, t1, t2 addq v0, t2, v0
ldq t1, 24(a1) addq v0, t0, v0 cmpult v0, t0, t2 addq v0, t2, v0
ldq t0, 32(a1) addq v0, t1, v0 cmpult v0, t1, t2 addq v0, t2, v0
ldq t1, 40(a1) addq v0, t0, v0 cmpult v0, t0, t2 addq v0, t2, v0
ldq t0, 48(a1) addq v0, t1, v0 cmpult v0, t1, t2 addq v0, t2, v0
ldq t1, 56(a1) addq v0, t0, v0 cmpult v0, t0, t2 addq v0, t2, v0
addq a1, 64, a1 addq v0, t1, v0 cmpult v0, t1, t2 addq v0, t2, v0.set reorder
beq t4, 40f // if zero, end of block
35: ldq t0, 0(a1)//// The following loop is allowed to be reordered by the assembler for// optimal scheduling. It is never branched into.// subq t4, 64, t4 // reduce byte count of longwords
ldq t1, 8(a1) addq v0, t0, v0 cmpult v0, t0, t2 addq v0, t2, v0
ldq t0, 16(a1) addq v0, t1, v0 cmpult v0, t1, t2 addq v0, t2, v0
ldq t1, 24(a1) addq v0, t0, v0 cmpult v0, t0, t2 addq v0, t2, v0
ldq t0, 32(a1) addq v0, t1, v0 cmpult v0, t1, t2 addq v0, t2, v0
ldq t1, 40(a1) addq v0, t0, v0 cmpult v0, t0, t2 addq v0, t2, v0
ldq t0, 48(a1) addq v0, t1, v0 cmpult v0, t1, t2 addq v0, t2, v0
ldq t1, 56(a1) addq v0, t0, v0 cmpult v0, t0, t2 addq v0, t2, v0
addq a1, 64, a1 addq v0, t1, v0 cmpult v0, t1, t2 addq v0, t2, v0
bne t4, 35b // if ne zero, not end of block
40://// Check for any remaining bytes.// and a2, 7, a2 // isolate residual bytes beq a2, 60f // if eq, no residual bytes50://// Checksum remaining bytes.//// The technique we use here is to load the final quadword, then// zero out the bytes that are not included.// ldq t0, 0(a1) // get quadword surrounding remainder55: ornot zero, zero, t1 // get FF mask sll t1, a2, t2 // shift to produce byte mask zap t0, t2, t0 // zero out bytes past end of buffer addq v0, t0, v0 // add quadword to partial checksum cmpult v0, t0, t1 // generate carry addq t1, v0, v0 // add carry back into checksum60://// Byte swap the 64-bit checksum if the start of the buffer was not word aligned// blbc t6, 65f zap v0, 0xAA, t0 // isolate even bytes sll t0, 8, t0 // shift even bytes into odd positions srl v0, 8, t1 // shift odd bytes into even positions zap t1, 0xAA, t1 // isolate odd bytes bis t0, t1, v0 // merge bytes back together
65://// add computed checksum to original checksum, and fold the 64-bit// result down to 16 bits.// addq v0, a0, v0 // add computed checksum to original cmpult v0, a0, t0 // generate carry addq v0, t0, v0 // add carry back into checksum
//// swap the longwords in order to sum two longwords and their carry in one add.// sll v0, 32, t0 // shift low longword into high srl v0, 32, t1 // shift high longword into low bis t1, t0, t5 // merge back together
addq v0, t5, t0 // produce sum + carry in high longword srl t0, 32, t1 // shift back down to low half//// swap the words in order to sum two words and their carry in one add// sll t1, 16, t2 // shift high word into low srl t1, 16, t3 // shift low word into high bis t2, t3, t4 // merge back together addq t4, t1, t2 // produce sum and carry in high word extwl t2, 2, v0 // extract result. ret zero, (ra) // return
.end tcpxsum
|
