Solidity inline assembly code for converting a hex string into the same bytes32

hexStringToBytes32.sol

/* Converts a hexadecimal string, whose bytes equivalent length 
can be up to 32 bytes (at least only tested and meant for up to 32 bytes)
into a bytes32 type.

EXAMPLE I/O
I: "a0c3689df9ce9c3aee5c1ba34dd1649098e2a10f6b2b337bf26695318cc0b958"
O: bytes32: 0xa0c3689df9ce9c3aee5c1ba34dd1649098e2a10f6b2b337bf26695318cc0b958

Currently assumes the 0x prefix is omitted from the string.

Written in ASM for low gas footprint
*/

contract hexStringToBytes32 {
    function parse(string _m) returns(bytes32) {
        bytes memory x = bytes(_m);
        uint len = x.length;
        delete x;
        assembly
        {
            let n := len
            len := sub(len, 1)
            let b := 0
            let o := 0
            let r := 0
        loop:
            n := sub(n, 1)
            div(n, 0x20) 0x20 mul 0x20 add _m add mload
            mod(n, 0x20)
            byte
            =: b
            // ensures valid hexadecimal character
            jumpi(invalidJumpLabel, lt(b, 0x30)) //can disable these checks to save some gas
            jumpi(num, lt(b, 0x3A))
            jumpi(invalidJumpLabel, lt(b, 0x41)) //can disable these checks to save some gas
            jumpi(ualpha, lt(b, 0x47))
            jumpi(invalidJumpLabel, lt(b, 0x61)) //can disable these checks to save some gas
            jumpi(lalpha, lt(b, 0x67))
            jump(invalidJumpLabel)
        num: 
            o := 0x30
            jump(loopcalc)
        lalpha:
            o := 0x57
            jump(loopcalc)
        ualpha:
            o := 0x37
            jump(loopcalc)
        loopcalc:
            sub(b, o)
            sub(len, n) 0x10 exp mul r add 
            =: r
            n 0 eq 1 sub
            loop
            jumpi
        loopend:
            0x0
            mstore
            return(0, 0x20)
        }
    }
}

this was written for solc 0.4.x or 0.5 back in the day iirc. A number of these low-level methodologies are not supported anymore in the most recent version of solidity. There is something called Huff which replicates working directly on the stack with EVM opcodes, or utilize the older solc which supports this.