Convert 16bit 2's complement number into standard number

[cymplecy]

My maths brain has locked up

given a 2 element list [255,254] which in hex represents 0xFFFE and if we assume it's in two's complement == -2

how can I get the two's complement decimal number of any [x,y] list

[d4s_over_dt4]

The easy way:
unsigned short x=a[0]*1<<8+a[1];
short y=*(*short)&x;
The hard way:
x=a[0]*1<<8+a[1];
if(x&1<<15)x-=1<<16;

(why don't we have pointers and explicit type conversion in snap?)

[cymplecy]

My brain started working again and I've come up with this

[edit] made a couple of custom reporters to tidy it up