GIF loader bug fix
Hi all!
The GIF loader I posted to this list recently contained a bug that
would in rare cases cause it to crash. I have just fixed this, so
here's the new code:
-------------------------------------------
include machine.e
include file.e
global constant PCX_OPEN_FAILED=1,
PCX_UNEXPECTED_EOF=2,
PCX_UNSUPPORTED_FORMAT=3,
GIF_OPEN_FAILED=1,
GIF_UNEXPECTED_EOF=2,
GIF_UNSUPPORTED_FORMAT=3
object junk
sequence image,the_palette,bit_table
integer file_num,exit_flag,palette_at_end
integer x_size,y_size,bits_per_pixel,n_colors
integer background,bytes_per_line,x_min,x_max
integer y_min,y_max,n_planes
bit_table=repeat({},256)
for n=0 to 255 do
bit_table[n+1]=int_to_bits(n,8)
end for
function read_bytes(integer amount)
sequence bytes
bytes=repeat(0,amount)
for b=1 to amount do
bytes[b]=getc(file_num)
if bytes[b]=-1 then
exit_flag=GIF_UNEXPECTED_EOF
end if
end for
return bytes
end function
function bytes_left()
integer place,end_place
place=where(file_num)
if seek(file_num,-1)=0 then
end_place=where(file_num)
if seek(file_num,place)=0 then
return end_place-place
else
return -1
end if
else
return -1
end if
end function
procedure read_pcx_header()
if bytes_left()<128 then
exit_flag=PCX_UNEXPECTED_EOF
return
end if
junk=getc(file_num)
palette_at_end=0
if getc(file_num)=5 then
palette_at_end=1
end if
if getc(file_num)!=1 then
exit_flag=PCX_UNSUPPORTED_FORMAT
return
end if
bits_per_pixel=getc(file_num)
if bits_per_pixel!=1 and bits_per_pixel!=8 then
exit_flag=PCX_UNSUPPORTED_FORMAT
return
end if
x_min=getc(file_num)+getc(file_num)*256
y_min=getc(file_num)+getc(file_num)*256
x_max=getc(file_num)+getc(file_num)*256
y_max=getc(file_num)+getc(file_num)*256
x_size=x_max-x_min+1
y_size=y_max-y_min+1
junk=read_bytes(4)
the_palette={}
if palette_at_end then
junk=read_bytes(48)
else
for c=1 to 16 do
the_palette=append(the_palette,read_bytes(3))
end for
end if
if exit_flag then
return
end if
if getc(file_num) then
exit_flag=PCX_UNSUPPORTED_FORMAT
return
end if
n_planes=getc(file_num)
bytes_per_line=getc(file_num)+getc(file_num)*256
junk=read_bytes(6)
for x=1 to 54 do
junk=getc(file_num)
if junk=-1 then
exit_flag=PCX_UNEXPECTED_EOF
return
elsif junk then
exit_flag=PCX_UNSUPPORTED_FORMAT
return
end if
end for
end procedure
procedure read_pcx_image()
sequence one_row,bits,new_row
integer number,byte,line,count,and_value,place
integer plane_power,amount
image=repeat({},y_size)
one_row=repeat(0,bytes_per_line*n_planes)
line=1
while line<=y_size do
number=1
while number<=length(one_row) do
byte=getc(file_num)
if byte=-1 then
exit_flag=PCX_UNEXPECTED_EOF
return
end if
if byte>191 then
count=byte-193
byte=getc(file_num)
if byte=-1 then
exit_flag=PCX_UNEXPECTED_EOF
return
end if
one_row[number..number+count]=byte
number=number+count+1
else
one_row[number]=byte
number=number+1
end if
end while
if bits_per_pixel=1 then
bits=repeat(0,bytes_per_line*8*n_planes)
place=1
for p=0 to n_planes-1 do
plane_power=power(2,p)
for t=1 to bytes_per_line do
byte=one_row[p*bytes_per_line+t]
and_value=256
for z=1 to 8 do
and_value=and_value/2
if and_bits(byte,and_value) then
bits[place]=plane_power
end if
place=place+1
end for
end for
end for
amount=bytes_per_line*8
new_row=bits[1..amount]
for p=1 to n_planes-1 do
new_row=new_row+bits[amount*p+1..amount*(p+1)]
end for
if length(new_row)>x_size then
new_row=new_row[1..x_size]
end if
else
new_row=one_row
end if
image[line]=new_row
line=line+1
end while
if palette_at_end then
junk=getc(file_num)
for c=1 to 256 do
the_palette=append(the_palette,read_bytes(3))
if find(-1,the_palette[c]) then
exit_flag=PCX_UNEXPECTED_EOF
return
end if
end for
end if
end procedure
procedure read_gif_header()
object work
sequence stuff,bits
integer global_color_map
if bytes_left()<6 then
exit_flag=GIF_UNEXPECTED_EOF
return
end if
stuff=read_bytes(3)
if compare(stuff,"GIF") and compare(stuff,"GIF") then
exit_flag=GIF_UNSUPPORTED_FORMAT
return
end if
junk=read_bytes(3)
if bytes_left()<7 then
exit_flag=GIF_UNEXPECTED_EOF
return
end if
junk=read_bytes(4)
bits=bit_table[getc(file_num)+1]
global_color_map=bits[8]
bits_per_pixel=bits_to_int(bits[1..3])+1
n_colors=power(2,bits_per_pixel)
background=getc(file_num)
junk=getc(file_num)
the_palette={}
if global_color_map then
if bytes_left()<n_colors*3 then
exit_flag=GIF_UNEXPECTED_EOF
return
end if
for c=1 to n_colors do
the_palette=append(the_palette,read_bytes(3))
end for
end if
while 1 do
work=getc(file_num)
if work=-1 then
exit_flag=GIF_UNEXPECTED_EOF
return
elsif work=',' then
exit
end if
end while
end procedure
procedure read_gif_image()
object work
sequence strings,bits,output,work_bits,string,stream
integer interlace,code_size,clear_code,end_of_info
integer num_bits,code,old,done,pointer,block_length
integer bit_add
if bytes_left()<9 then
exit_flag=GIF_UNEXPECTED_EOF
return
end if
junk=read_bytes(4)
x_size=getc(file_num)+getc(file_num)*256
y_size=getc(file_num)+getc(file_num)*256
work=getc(file_num)
bits=bit_table[work+1]
if bits[8] then
bits_per_pixel=bits_to_int(bits[1..3])+1
n_colors=power(2,bits_per_pixel)
the_palette={}
for c=1 to n_colors do
the_palette=append(the_palette,read_bytes(3))
end for
if exit_flag then
return
end if
end if
interlace=bits[7]
image=repeat({},y_size)
output={}
if n_colors=2 then
n_colors=4
end if
strings=repeat({},n_colors+2)
for t=1 to n_colors do
strings[t]={t-1}
end for
code_size=getc(file_num)
if code_size=-1 then
exit_flag=GIF_UNEXPECTED_EOF
return
end if
clear_code=power(2,code_size)+1
end_of_info=clear_code+1
num_bits=code_size+1
stream={}
while 1 do
block_length=getc(file_num)
if block_length=0 then
exit
end if
for b=1 to block_length do
stream=append(stream,getc(file_num))
end for
end while
if find(-1,stream) then
exit_flag=GIF_UNEXPECTED_EOF
return
end if
stream=append(stream,0)
stream=append(stream,-1)
pointer=1
bits={}
while length(bits)<26 do
bits=bits & bit_table[stream[pointer]+1]
pointer=pointer+1
end while
bits=bits[num_bits+1..length(bits)]
work_bits=bits[1..num_bits]
code=bits_to_int(work_bits)+1
output=strings[code]
old=code
bits=bits[num_bits+1..length(bits)]
done=0
while 1 do
while length(bits)<26 and done=0 do
work=stream[pointer]
pointer=pointer+1
if work=-1 then
done=1
exit
end if
bits=bits & bit_table[work+1]
end while
if length(bits)<num_bits then
exit
end if
code=1
bit_add=1
for b=1 to num_bits do
if bits[b] then
code=code+bit_add
end if
bit_add=bit_add+bit_add
end for
bits=bits[num_bits+1..length(bits)]
if code=end_of_info then
exit
elsif code=clear_code then
strings=repeat({},n_colors+2)
for t=1 to n_colors do
strings[t]={t-1}
end for
num_bits=code_size+1
work_bits=bits[1..num_bits]
code=bits_to_int(work_bits)+1
for t=1 to length(strings[code]) do
output=append(output,strings[code][t])
end for
old=code
bits=bits[num_bits+1..length(bits)]
else
if code<=length(strings) then
string=strings[code]
for t=1 to length(string) do
output=append(output,string[t])
end for
work=strings[old] & string[1]
strings=append(strings,work)
old=code
else
work=strings[old] & strings[old][1]
for t=1 to length(work) do
output=append(output,work[t])
end for
strings=append(strings,work)
old=code
end if
end if
if length(strings)=power(2,num_bits) then
num_bits=num_bits+1
if num_bits=13 then
num_bits=12
end if
end if
end while
work=repeat({},y_size)
for r=0 to y_size-1 do
work[r+1]=output[r*x_size+1..r*x_size+x_size]
end for
if interlace then
image=repeat({},y_size)
pointer=1
for l=1 to y_size by 8 do
image[l]=work[pointer]
pointer=pointer+1
end for
for l=5 to y_size by 8 do
image[l]=work[pointer]
pointer=pointer+1
end for
for l=3 to y_size by 4 do
image[l]=work[pointer]
pointer=pointer+1
end for
for l=2 to y_size by 2 do
image[l]=work[pointer]
pointer=pointer+1
end for
else
image=work
end if
end procedure
global function read_pcx(sequence filename)
exit_flag=0
file_num=open(filename,"rb")
if file_num<0 then
return PCX_OPEN_FAILED
end if
read_pcx_header()
if exit_flag then
close(file_num)
return exit_flag
end if
read_pcx_image()
close(file_num)
if exit_flag then
return exit_flag
end if
the_palette=the_palette[1..power(2,bits_per_pixel*n_planes)]
return {the_palette,image}
end function
global function read_gif(sequence file_name)
exit_flag=0
file_num=open(file_name,"rb")
if file_num<0 then
return GIF_OPEN_FAILED
end if
read_gif_header()
if exit_flag then
close(file_num)
return exit_flag
end if
read_gif_image()
close(file_num)
if exit_flag then
return exit_flag
end if
return {the_palette,image}
end function
-------------------------------------------
Regards,
Michael Bolin
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