inflate: Fix handling of zero-length uncompressed block

This is a silly case presumably caused by a buggy or unoptimised compressor, but it has been seen in practice and it is not explicitly disallowed by RFC 1951.
keirf · Feb 10, 2025 · 6c79397 · 6c79397
1 parent ae428d4
commit 6c79397
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Showing 2 changed files with 4 additions and 4 deletions.
diff --git a/inflate/inflate.S b/inflate/inflate.S
@@ -423,9 +423,9 @@ uncompressed_block:
         moveq   #16,d1
         jbsr    stream_next_bits /* LEN */
         addq.w  #2,a5           /* skip NLEN */
-        subq.w  #1,d0           /* d0.w = len-1 (for dbf) */
+        jra     2f              /* decrement LEN for DBF loop */
 1:      move.b  (a5)+,(a4)+
-        dbf     d0,1b
+2:      dbf     d0,1b
         rts
 
 #define o_hdist /*0*/

diff --git a/inflate/inflate.asm b/inflate/inflate.asm
@@ -433,9 +433,9 @@ uncompressed_block:
         moveq   #16,d1
         bsr     stream_next_bits ; LEN
         addq.w  #2,a5           ; skip NLEN
-        subq.w  #1,d0           ; d0.w = len-1 (for dbf)
+        bra     .2              ; decrement LEN for DBF loop
 .1:     move.b  (a5)+,(a4)+
-        dbf     d0,.1
+.2:     dbf     d0,.1
         rts
 
 o_hdist = 0