zXc developments » ASM http://www.zxcdev.com Enveloped by Code Mon, 24 May 2010 22:41:17 +0000 en hourly 1 http://wordpress.org/?v=3.0 One-Hot State Decoder http://www.zxcdev.com/2009/06/one-hot-state-decoder/ http://www.zxcdev.com/2009/06/one-hot-state-decoder/#comments Sat, 06 Jun 2009 15:12:48 +0000 Shawn http://zxcdev.com/?p=15 Here is a quick way for you to decode a one hot state value into a binary representation. This code is built for the MIPS32 architecture.

/*************************************
* One-Hot Decoder
*      Usage: Convert the lower nibble of a 32bit
*            one hot active low to a binary number
*            representing the bit position.
*      Input: $a0 for the hot value (IE: 0b1101)
*     Output: $v0 is the decoded value (IE: 0x1)
*************************************/
.ent one_hot_decode
one_hot_decode:
        //Invert the incoming ( Remove if Active High )
        xori    $a0, $a0, 0xF
 
        //Count the number of leading zeros
        clz             $t1, $a0
 
        //v0 = 31 - #zeros
        li              $t0, 31
        subu    $v0, $t0, $t1
 
        jr              $ra
        nop
.end one_hot_decode
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