Código fuente de 'Checksum.asp'
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<title>Checksum - Códigos asp, programacion asp, descargas asp, rutinas asp</title>
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<center><b><font face="Arial" size="3">Checksum</font></b></center><br>
En un programa simple de detección de errores, cada mensaje transmitido se
acompaña por un valor numérico basado en el número de bits a 1 del mensaje. La
estación receptora del mensaje aplica la misma fórmula al mensaje y comprueba si
el valor numérico que acompaña al mensajes es el mismo. Si no, el receptor
concluye que el mensaje es erróneo o ha sido manipulado.<br>
<br>
Este script permite calcular el CRC Checksum o valor numérico de los mensajes
transmitidos.<br>
<br>
<!-- '**************************************
A simple error-detection scheme in which each transmitted message is accompanied by a numerical
value based on the number of set bits in the message.
The receiving station then applies the same formula to the message and checks to make sure the
accompanying numerical value is the same. If not, the receiver can assume that the message
has been garbled.
' Name: CRC Checksum - Description:Calculates the CRC for a given string.
' By: Leigh Bowers
' Returns:A long representing the CRC checksum.
' http://www.Planet-Source-Code.com/vb/scripts/ShowCode.asp?txtCodeId=7219&lngWId=4
-->
<%
function shr(plValue, pbBits)
' Shift bits to the right by <pbBits&
' gt;
shr = plValue \ (2 ^ pbBits)
End function
function CalculateCRC(psString)
Dim sValues, alCRCTable, lCRC
Dim l
sValues = "&h0,&h77073096,&hEE0E612C,&h990951BA,&h076DC419,&h706AF48F,&hE963A535,&h9E6495A3,&h0EDB8832,&h79DCB8A4,&hE0D5E91E,&h97D2D988,&h09B64C2B,&h7EB17CBD,&hE7B82D07,&h90BF1D91,&h1DB71064,&h6AB020F2,&hF3B97148,&h84BE41DE,&h1ADAD47D,&h6DDDE4EB,&hF4D4B551,&h83D385C7,&h136C9856,&h646BA8C0,&hFD62F97A,&h8A65C9EC,&h14015C4F,&h63066CD9,&hFA0F3D63,&h8D080DF5,&h3B6E20C8,&h4C69105E,&hD56041E4,&hA2677172,&h3C03E4D1,&h4B04D447," _
+ "&hD20D85FD,&hA50AB56B,&h35B5A8FA,&h42B2986C,&hDBBBC9D6,&hACBCF940,&h32D86CE3,&h45DF5C75,&hDCD60DCF,&hABD13D59,&h26D930AC,&h51DE003A,&hC8D75180,&hBFD06116,&h21B4F4B5,&h56B3C423,&hCFBA9599,&hB8BDA50F,&h2802B89E,&h5F058808,&hC60CD9B2,&hB10BE924,&h2F6F7C87,&h58684C11,&hC1611DAB,&hB6662D3D,&h76DC4190,&h01DB7106,&h98D220BC,&hEFD5102A,&h71B18589,&h06B6B51F,&h9FBFE4A5,&hE8B8D433,&h7807C9A2,&h0F00F934,&h9609A88E,&hE10E9818," _
+ "&h7F6A0DBB,&h086D3D2D,&h91646C97,&hE6635C01,&h6B6B51F4,&h1C6C6162,&h856530D8,&hF262004E,&h6C0695ED,&h1B01A57B,&h8208F4C1,&hF50FC457,&h65B0D9C6,&h12B7E950,&h8BBEB8EA,&hFCB9887C,&h62DD1DDF,&h15DA2D49,&h8CD37CF3,&hFBD44C65,&h4DB26158,&h3AB551CE,&hA3BC0074,&hD4BB30E2,&h4ADFA541,&h3DD895D7,&hA4D1C46D,&hD3D6F4FB,&h4369E96A,&h346ED9FC,&hAD678846,&hDA60B8D0,&h44042D73,&h33031DE5,&hAA0A4C5F,&hDD0D7CC9,&h5005713C,&h270241AA," _
+ "&hBE0B1010,&hC90C2086,&h5768B525,&h206F85B3,&hB966D409,&hCE61E49F,&h5EDEF90E,&h29D9C998,&hB0D09822,&hC7D7A8B4,&h59B33D17,&h2EB40D81,&hB7BD5C3B,&hC0BA6CAD,&hEDB88320,&h9ABFB3B6,&h03B6E20C,&h74B1D29A,&hEAD54739,&h9DD277AF,&h04DB2615,&h73DC1683,&hE3630B12,&h94643B84,&h0D6D6A3E,&h7A6A5AA8,&hE40ECF0B,&h9309FF9D,&h0A00AE27,&h7D079EB1,&hF00F9344,&h8708A3D2,&h1E01F268,&h6906C2FE,&hF762575D,&h806567CB,&h196C3671,&h6E6B06E7," _
+ "&hFED41B76,&h89D32BE0,&h10DA7A5A,&h67DD4ACC,&hF9B9DF6F,&h8EBEEFF9,&h17B7BE43,&h60B08ED5,&hD6D6A3E8,&hA1D1937E,&h38D8C2C4,&h4FDFF252,&hD1BB67F1,&hA6BC5767,&h3FB506DD,&h48B2364B,&hD80D2BDA,&hAF0A1B4C,&h36034AF6,&h41047A60,&hDF60EFC3,&hA867DF55,&h316E8EEF,&h4669BE79,&hCB61B38C,&hBC66831A,&h256FD2A0,&h5268E236,&hCC0C7795,&hBB0B4703,&h220216B9,&h5505262F,&hC5BA3BBE,&hB2BD0B28,&h2BB45A92,&h5CB36A04,&hC2D7FFA7,&hB5D0CF31," _
+ "&h2CD99E8B,&h5BDEAE1D,&h9B64C2B0,&hEC63F226,&h756AA39C,&h026D930A,&h9C0906A9,&hEB0E363F,&h72076785,&h05005713,&h95BF4A82,&hE2B87A14,&h7BB12BAE,&h0CB61B38,&h92D28E9B,&hE5D5BE0D,&h7CDCEFB7,&h0BDBDF21,&h86D3D2D4,&hF1D4E242,&h68DDB3F8,&h1FDA836E,&h81BE16CD,&hF6B9265B,&h6FB077E1,&h18B74777,&h88085AE6,&hFF0F6A70,&h66063BCA,&h11010B5C,&h8F659EFF,&hF862AE69,&h616BFFD3,&h166CCF45,&hA00AE278,&hD70DD2EE,&h4E048354,&h3903B3C2," _
+ "&hA7672661,&hD06016F7,&h4969474D,&h3E6E77DB,&hAED16A4A,&hD9D65ADC,&h40DF0B66,&h37D83BF0,&hA9BCAE53,&hDEBB9EC5,&h47B2CF7F,&h30B5FFE9,&hBDBDF21C,&hCABAC28A,&h53B39330,&h24B4A3A6,&hBAD03605,&hCDD70693,&h54DE5729,&h23D967BF,&hB3667A2E,&hC4614AB8,&h5D681B02,&h2A6F2B94,&hB40BBE37,&hC30C8EA1,&h5A05DF1B,&h2D02EF8D"
alCRCTable = Split(sValues, ",")
lCRC = &hFFFFFFFF
For l = 1 To Len(psString)
lCRC = alCRCTable(((lCRC And &hFFFF) Xor Asc(Mid(psString, l, 1))) And &hFF) Xor shr(lCRC, 8)
Next ' l
lCRC = lCRC Xor &hFFFFFFFF
CalculateCRC = lCRC
End function
Response.Write "Cálculo del checksum (para una dirección de Internet cualquiera) --> <br>" & _
"Hex(CalculateCRC(""http://www.google.com"") = " & "$" & Hex(CalculateCRC("http://www.google.com"))
%>