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Update 8_1_Understanding_the_Foundation_of_P2SH.md

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8_1_Understanding_the_Foundation_of_P2SH.md
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@ -67,6 +67,8 @@ _Why are P2SH scripts limited to 520 bytes?_ As with many things in Bitcoin, the
Serializing a locking script is a two-part process. First, you must turn it into hexcode, then you must transform that hex into binary. Serializing a locking script is a two-part process. First, you must turn it into hexcode, then you must transform that hex into binary.
_If what follows looks intimidating, don't worry about it; this will usually be done with an API. As we lay bare the foundation of P2SH Scripting, we're mostly explaining what those APIs will do._
#### Create the Hex Code #### Create the Hex Code
Creating the hexcode that is necessary to serialize a script is both a simple translation and something that's complex enough that it goes beyond any shell script that you're likely to write. As with a few other aspects of P2SH scripts, it's something that you'll probably process through an API, not by hand. Creating the hexcode that is necessary to serialize a script is both a simple translation and something that's complex enough that it goes beyond any shell script that you're likely to write. As with a few other aspects of P2SH scripts, it's something that you'll probably process through an API, not by hand.
@ -92,7 +94,7 @@ $ hex=$(printf '%08x\n' $integer | sed 's/^\(00\)*//')
$ echo $hex $ echo $hex
5c2a7b9f 5c2a7b9f
``` ```
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. Third, you need to add a top 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) $ hexfirst=$(echo $hex | cut -c1)
$ [[ 0x$hexfirst -gt 0x7 ]] && hex="00"$hex $ [[ 0x$hexfirst -gt 0x7 ]] && hex="00"$hex
@ -103,7 +105,7 @@ $ lehex=$(echo $hex | tac -rs .. | echo "$(tr -d '\n')")
$ echo $lehex $ echo $lehex
9f7b2a5c 9f7b2a5c
``` ```
In addition, you'll always need to know the size of your constants. You can just remember that every two hexidecimal characters is one byte. Or, you can use `echo -n` piped to `wc -c`, and divide that in two: In addition, you'll always need to know the size of your integers. You can just remember that every two hexidecimal characters is one byte. Or, you can use `echo -n` piped to `wc -c`, and divide that in two:
``` ```
$ echo -n $lehex | wc -c | awk '{print $1/2}' $ echo -n $lehex | wc -c | awk '{print $1/2}'
4 4
@ -117,8 +119,6 @@ $ echo $neglehex
9f7b2adc 9f7b2adc
``` ```
_If this is intimidating, don't worry about it; as we said, this will usually be done with an API. As we lay bare the foundation of P2SH Scripting, we're mostly explaining what those APIs will do._
#### Create the Hex Code: A Multisig Example #### Create the Hex Code: A Multisig Example
It may be easier to understand this by taking an existing hexcode and translating it back to Bitcoin Script. For example, look at the `redeemScript` that you used [§6.1](6_1_Sending_a_Transaction_to_a_Multisig.md): It may be easier to understand this by taking an existing hexcode and translating it back to Bitcoin Script. For example, look at the `redeemScript` that you used [§6.1](6_1_Sending_a_Transaction_to_a_Multisig.md):