--- trunk/xvidcore/src/bitstream/ppc_asm/cbp_ppc.s	2002/03/22 04:37:03	53
+++ trunk/xvidcore/src/bitstream/ppc_asm/cbp_ppc.s	2002/03/22 11:29:20	54
@@ -1,4 +1,4 @@
-#    Copyright (C) 2002 Guillaume Morin, Alcôve
+#    Copyright (C) 2002 Guillaume Morin <guillaume@morinfr.org>, Alcôve
 #
 #    This program is free software; you can redistribute it and/or modify
 #    it under the terms of the GNU General Public License as published by
@@ -15,60 +15,82 @@
 #    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 #
 #
-#    $Id: cbp_ppc.s,v 1.1 2002-03-21 23:42:53 canard Exp $
+#    $Id: cbp_ppc.s,v 1.2 2002-03-22 11:29:20 canard Exp $
 #    $Source: /home/xvid/cvs_copy/cvs-server-root/xvid/xvidcore/src/bitstream/ppc_asm/cbp_ppc.s,v $
-#    $Date: 2002-03-21 23:42:53 $
+#    $Date: 2002-03-22 11:29:20 $
 #    $Author: canard $
+#
+#    This is my first PPC ASM program. So I might do nasty things.
+#    Please send any comments to guillaume@morinfr.org
+
 
-#uint32_t calc_cbp_c(const int16_t codes[6][64])
+# Returns a field of bits that indicates non zero ac blocks
+# for this macro block
+#
+# uint32_t calc_cbp_c(const int16_t codes[6][64])
 #{
-#    uint32_t i, j;
-#    uint32_t cbp = 0;
+#	uint32_t i, j;
+#	uint32_t cbp = 0;
 #
-#    for (i = 0; i < 6; i++) {
-#		for (j = 1; j < 64/4; j+=4) {
+#	for (i = 0; i < 6; i++) {
+#		for (j = 1; j < 61; j+=4) {
 #			if (codes[i][j]  |codes[i][j+1]|
-#				codes[i][j+2]|codes[i][j+3]) {
+#			    codes[i][j+2]|codes[i][j+3]) {
 #				cbp |= 1 << (5 - i);
 #				break;
 #			}
 #		}
-#    }
-#    return cbp;
+#
+#		if(codes[i][j]|codes[i][j+1]|codes[i][j+2])
+#			cbp |= 1 << (5 - i);
+#
+#	}
+#
+#	return cbp;
+#
 #}
 
 .text
 .global calc_cbp_ppc
 calc_cbp_ppc:
+	# r9 will contain coeffs addr
 	mr 9,3
+	# r8 is the loop counter
 	li 8,5
+	# r3 contains the result, therefore we set it to 0
 	xor 3,3,3
 .loop:
+	# r7 is the loop2 counter, FIXME: use CTR
 	li 7,14
+	# r6 is coeff pointer for this line
 	mr 6,9
 .loop2:
+	# coeffs is a matrix of 16 bits cells
 	lha 4,2(6)
 	lha 5,4(6)
 	or 4,5,4
 	lha 5,6(6)
 	or 4,5,4
 	lha 5,8(6)
-	or 4,5,4
-	cmpwi 4,0
-	bne .cbp
+	# or. updates CR0
+	or. 4,5,4
+	# testing bit 2 (is zero) of CR0
+	bc 4,2,.cbp
 	addi 6,6,8
-	subi 7,7,1
-	cmpwi 7,-1
-	beq .lastcoeffs
+	# subic. updates CR0
+	subic. 7,7,1
+	# testing bit 0 (is negative) of CR0
+	bc 12,0,.lastcoeffs
 	b .loop2
 .lastcoeffs:
 	lha 4,2(6)
 	lha 5,4(6)
 	or 4,5,4
 	lha 5,6(6)
-	or 4,5,4
-	cmpwi 4,0
-	beq .newline
+	# or. updates CR0
+	or. 4,5,4
+	# testing bit 2 (is zero) of CR0
+	bc 12,2,.newline
 .cbp:
 	li 4,1
 	slw 4,4,8
@@ -76,8 +98,8 @@
 	b .newline
 .newline:
 	addi 9,9,128
-	subi 8,8,1
-	cmpwi 8,-1
-	bne .loop
+	# updates CR0, blabla
+	subic. 8,8,1
+	bc 4,0,.loop
 .end:
 	blr