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Update 8_1_Understanding_the_Foundation_of_P2SH.md

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Shannon Appelcline 2017-05-25 14:22:30 -07:00 committed by GitHub
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8_1_Understanding_the_Foundation_of_P2SH.md
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@ -92,7 +92,12 @@ $ hex=$(printf '%08x\n' $integer | sed 's/^\(00\)*//')
$ echo $hex $ echo $hex
5c2a7b9f 5c2a7b9f
``` ```
Third, you need to translate the hex from big-endian (least significant byte last) to little-endian (least significant byte first). You can do this with the `tac` command (or by hand if you prefer): Third, you need to add a byte of `00` if the top digit is "8" or greater, so that it's not interpretted as a negative number.
```
$ hexfirst=$(echo $hex | cut -c1)
$ [[ 0x$hexfirst -gt 0x7 ]] && hex="00"$hex
```
Fourth, you need to translate the hex from big-endian (least significant byte last) to little-endian (least significant byte first). You can do this with the `tac` command (or by hand if you prefer):
``` ```
$ lehex=$(echo $hex | tac -rs .. | echo "$(tr -d '\n')") $ lehex=$(echo $hex | tac -rs .. | echo "$(tr -d '\n')")
$ echo $lehex $ echo $lehex
@ -206,7 +211,7 @@ _What is the power of P2SH?_ You already know the power of Bitcoin Script, which
## Appendix: The Integer Conversion Script ## Appendix: The Integer Conversion Script
The following script collects the collect methodology for changing an integer to -2147483647 and 2147483647 to a little-endian signed-magnitude representation: The following script collects the complete methodology for changing an integer between -2147483647 and 2147483647 to a little-endian signed-magnitude representation:
``` ```
file: integer2lehex.sh file: integer2lehex.sh
#!/bin/bash #!/bin/bash
@ -232,8 +237,11 @@ else
negative=0; negative=0;
fi fi
hex=$(printf '%08x\n' $integer | sed 's/^\(00\)*//'); hex=$(printf '%08x\n' $integer | sed 's/^\(00\)*//');
hexfirst=$(echo $hex | cut -c1)
[[ 0x$hexfirst -gt 0x7 ]] && hex="00"$hex
lehex=$(echo $hex | tac -rs .. | echo "$(tr -d '\n')"); lehex=$(echo $hex | tac -rs .. | echo "$(tr -d '\n')");
if [ "$negative" -eq "1" ]; if [ "$negative" -eq "1" ];
@ -241,7 +249,6 @@ then
lehex=$(printf '%x\n' $((0x$lehex | 0x80))) lehex=$(printf '%x\n' $((0x$lehex | 0x80)))
fi fi
size=$(echo -n $lehex | wc -c | awk '{print $1/2}'); size=$(echo -n $lehex | wc -c | awk '{print $1/2}');
hexcodeprefix=$(printf '%02x\n' $size); hexcodeprefix=$(printf '%02x\n' $size);