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Variable-length quantity: Difference between revisions

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Variable-length quantity (view source)

Revision as of 19:16, 25 March 2021

9,375 bytes added ,  3 years ago
m
→‎{{header|Phix}}: added syntax colouring the hard way
m (→‎{{header|Phix}}: added syntax colouring the hard way)
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=={{header|Phix}}==
Copy of [[Variable-length_quantity#Euphoria|Euphoria]], modified to pack several numbers into a single stream. Also added an explicit check that (as per wp) only unsigned numbers are attempted.
 
<lang Phix>function vlq_encode(sequence s)
<!--<lang Phix>-->
sequence res = {}
<span style="color: #008080;">function</span> <span style="color: #000000;">vlq_encode</span><span style="color: #0000FF;">(</span><span style="color: #004080;">sequence</span> <span style="color: #000000;">s</span><span style="color: #0000FF;">)</span>
integer n, msb
<span style="color: #004080;">sequence</span> <span style="color: #000000;">res</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{}</span>
for i=length(s) to 1 by -1 do
<span style="color: #008080;">for</span> <span style="color: #000000;">i</span><span style="color: #0000FF;">=</span><span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">s</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">to</span> <span style="color: #000000;">1</span> <span style="color: #008080;">by</span> <span style="color: #0000FF;">-</span><span style="color: #000000;">1</span> <span style="color: #008080;">do</span>
n = s[i]
<span style="color: #004080;">integer</span> <span style="color: #000000;">n</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">s</span><span style="color: #0000FF;">[</span><span style="color: #000000;">i</span><span style="color: #0000FF;">],</span> <span style="color: #000000;">msb</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">0</span>
if n<0 then crash("unsigned integers only!") end if
<span style="color: #008080;">if</span> <span style="color: #000000;">n</span><span style="color: #0000FF;"><</span><span style="color: #000000;">0</span> <span style="color: #008080;">then</span> <span style="color: #7060A8;">crash</span><span style="color: #0000FF;">(</span><span style="color: #008000;">"unsigned integers only!"</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
msb = 0
<span style="color: #008080;">while</span> <span style="color: #000000;">1</span> <span style="color: #008080;">do</span>
while 1 do
<span style="color: #000000;">res</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">prepend</span><span style="color: #0000FF;">(</span><span style="color: #000000;">res</span><span style="color: #0000FF;">,</span><span style="color: #000000;">msb</span><span style="color: #0000FF;">+</span><span style="color: #7060A8;">and_bits</span><span style="color: #0000FF;">(</span><span style="color: #000000;">n</span><span style="color: #0000FF;">,</span><span style="color: #000000;">#7F</span><span style="color: #0000FF;">))</span>
res = prepend(res,msb+and_bits(n,#7F))
<span style="color: #000000;">n</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">floor</span><span style="color: #0000FF;">(</span><span style="color: #000000;">n</span><span style="color: #0000FF;">/</span><span style="color: #000000;">#80</span><span style="color: #0000FF;">)</span>
n = floor(n/#80)
<span style="color: #008080;">if</span> <span style="color: #000000;">n</span><span style="color: #0000FF;">=</span><span style="color: #000000;">0</span> <span style="color: #008080;">then</span> <span style="color: #008080;">exit</span> <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
if n=0 then exit end if
<span style="color: #000000;">msb</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">#80</span>
msb = #80
<span style="color: #008080;">end</span> <span style="color: #008080;">while</span>
end while
<span style="color: #008080;">end</span> <span style="color: #008080;">for</span>
end for
<span style="color: #008080;">return</span> <span style="color: #000000;">res</span>
return res
<span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
end function
<span style="color: #008080;">function</span> <span style="color: #000000;">vlq_decode</span><span style="color: #0000FF;">(</span><span style="color: #004080;">sequence</span> <span style="color: #000000;">s</span><span style="color: #0000FF;">)</span>
function vlq_decode(sequence s)
<span style="color: #004080;">sequence</span> <span style="color: #000000;">res</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{}</span>
sequence res = {}
<span style="color: #008080;">for</span> <span style="color: #000000;">i</span><span style="color: #0000FF;">=</span><span style="color: #000000;">1</span> <span style="color: #008080;">to</span> <span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">s</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">do</span>
integer n = 0, byte
<span style="color: #004080;">integer</span> <span style="color: #000000;">si</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">s</span><span style="color: #0000FF;">[</span><span style="color: #000000;">i</span><span style="color: #0000FF;">],</span>
for i=1 to length(s) do
<span style="color: #000000;">n</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">n</span><span style="color: #0000FF;">*</span><span style="color: #000000;">#80</span><span style="color: #0000FF;">+</span><span style="color: #7060A8;">and_bits</span><span style="color: #0000FF;">(</span><span style="color: #004080;">byte</span><span style="color: #0000FF;">,</span><span style="color: #000000;">#7F</span><span style="color: #0000FF;">)</span>
byte = s[i]
<span style="color: #008080;">if</span> <span style="color: #008080;">not</span> <span style="color: #7060A8;">and_bits</span><span style="color: #0000FF;">(</span><span style="color: #000000;">si</span><span style="color: #0000FF;">,</span><span style="color: #000000;">#80</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">then</span>
n = n*#80+and_bits(byte,#7F)
<span style="color: #000000;">res</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">append</span><span style="color: #0000FF;">(</span><span style="color: #000000;">res</span><span style="color: #0000FF;">,</span><span style="color: #000000;">n</span><span style="color: #0000FF;">)</span>
if not and_bits(byte,#80) then
<span style="color: #000000;">n</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">0</span>
res = append(res,n)
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
n = 0
<span style="color: #008080;">end</span> <span style="color: #008080;">for</span>
end if
<span style="color: #008080;">return</span> <span style="color: #000000;">res</span>
end for
<span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
return res
end function
<span style="color: #008080;">function</span> <span style="color: #000000;">svlg</span><span style="color: #0000FF;">(</span><span style="color: #004080;">sequence</span> <span style="color: #000000;">s</span><span style="color: #0000FF;">)</span>
<span style="color: #004080;">string</span> <span style="color: #000000;">res</span> <span style="color: #0000FF;">=</span> <span style="color: #008000;">""</span>
function svlg(sequence s)
<span style="color: #008080;">for</span> <span style="color: #000000;">i</span><span style="color: #0000FF;">=</span><span style="color: #000000;">1</span> <span style="color: #008080;">to</span> <span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">s</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">do</span>
string res = ""
<span style="color: #000000;">res</span> <span style="color: #0000FF;">&=</span> <span style="color: #7060A8;">sprintf</span><span style="color: #0000FF;">(</span><span style="color: #008000;">"#%02x:"</span><span style="color: #0000FF;">,{</span><span style="color: #000000;">s</span><span style="color: #0000FF;">[</span><span style="color: #000000;">i</span><span style="color: #0000FF;">]})</span>
for i=1 to length(s) do
<span style="color: #008080;">end</span> <span style="color: #008080;">for</span>
res &= sprintf("#%02x:",{s[i]})
<span style="color: #008080;">return</span> <span style="color: #000000;">res</span><span style="color: #0000FF;">[</span><span style="color: #000000;">1</span><span style="color: #0000FF;">..$-</span><span style="color: #000000;">1</span><span style="color: #0000FF;">]</span>
end for
<span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
return res[1..$-1]
end function
<span style="color: #008080;">constant</span> <span style="color: #000000;">testNumbers</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{</span> <span style="color: #000000;">#200000</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">#1FFFFF</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">1</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">127</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">128</span> <span style="color: #0000FF;">}</span>
<span style="color: #004080;">sequence</span> <span style="color: #000000;">s</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">vlq_encode</span><span style="color: #0000FF;">(</span><span style="color: #000000;">testNumbers</span><span style="color: #0000FF;">),</span>
constant testNumbers = { #200000, #1FFFFF, 1, 127, 128 }
<span style="color: #000000;">decoded</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">vlq_decode</span><span style="color: #0000FF;">(</span><span style="color: #000000;">s</span><span style="color: #0000FF;">)</span>
sequence s = vlq_encode(testNumbers)
<span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"%s -> %s -> %s\n"</span><span style="color: #0000FF;">,{</span><span style="color: #000000;">svlg</span><span style="color: #0000FF;">(</span><span style="color: #000000;">testNumbers</span><span style="color: #0000FF;">),</span><span style="color: #000000;">svlg</span><span style="color: #0000FF;">(</span><span style="color: #000000;">s</span><span style="color: #0000FF;">),</span><span style="color: #000000;">svlg</span><span style="color: #0000FF;">(</span><span style="color: #000000;">decoded</span><span style="color: #0000FF;">)})</span>
sequence decoded = vlq_decode(s)
<span style="color: #008080;">if</span> <span style="color: #000000;">decoded</span><span style="color: #0000FF;">!=</span><span style="color: #000000;">testNumbers</span> <span style="color: #008080;">then</span> <span style="color: #7060A8;">crash</span><span style="color: #0000FF;">(</span><span style="color: #008000;">"something wrong"</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
printf(1,"%s -> %s -> %s\n",{svlg(testNumbers),svlg(s),svlg(decoded)})
<!--</lang>-->
if decoded!=testNumbers then crash("something wrong") end if</lang>
 
{{out}}
<pre>
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