sh/lib/checksum.S

1 /* SPDX-License-Identifier: GPL-2.0+
32  * computes a partial checksum, e.g. for TCP/UDP fragments
43 	   * is aligned on either a 2-byte or 4-byte boundary.  We get at
44 	   * least a twofold speedup on 486 and Pentium if it is 4-byte aligned.
45 	   * Fortunately, it is easy to convert 2-byte alignment to 4-byte
50 	bt/s	2f		! Jump if alignment is ok.
51 	 mov	r4, r7		! Keep a copy to check for alignment
54 	bt	21f		! Jump if alignment is boundary of 2bytes.
58 	add	#-1, r5
59 	bt	9f
62 	addc	r0, r6		! t=0 from previous tst
70 	bt	2f
72 	! buf is 2 byte aligned (len could be 0)
73 	add	#-2, r5		! Alignment uses up two bytes.
75 	bt/s	1f		! Jump if we had at least two bytes.
77 	bra	6f
83 	bf	2f
86 	! buf is 4 byte aligned (len could be 0)
88 	mov	#-5, r0
91 	bt/s	4f		! if it's =0, go to 4f
115 	! here, we know r1==0
119 	and	#0x1c, r0
121 	bt	6f
125 	mov	#0, r2
134 	addc	r1, r6		! r1==0 here, so it means add carry-bit
140 	bt	9f		! if it's =0 go to 9f
143 	bf	7f
147 	bt/s	8f
159 	mov	#0, r0
161 9:
165 	bt	10f
181  * sum being ~0U
186 	.section __ex_table, "a";	\
187 	.long 9999b, 6001f	;	\
196 	mov	#-1,r7
202 	bf	3f		! Different alignments, use slow version
204 	bf	3f		! If not, do it the slow way
208 	bt	2f		! Jump if alignment is ok.
209 	add	#-2,r6		! Alignment uses up two bytes.
211 	bt/s	1f
214 	bra	4f
222 	bt	4f
246 	mov	#0,r0
251 	bt	7f
252 	bra	5f
255 	! src and dest equally aligned, but to a two byte boundary.
256 	! Handle first two bytes as a special case
264 	mov	#0,r0
268 	mov	#-5,r0
271 	bt/s	2f
307 	mov	#0,r0
311 	mov	#0x1c,r0
314 	bf/s	4f
326 	mov	#0,r0
332 	bf	7f
335 	bf	5f
341 	bt/s	6f
353 	mov	#0,r0
362 	 mov	#0,r0