zabbix has the following definitions :

common.h:#define ZBX_KIBIBYTE 1024
common.h:#define ZBX_MEBIBYTE 1048576
common.h:#define ZBX_GIBIBYTE 1073741824

tera is missing, thus misc.c does something a little bit ugly for T (assuming there isn't some specific reason for this ) :

factor = ZBX_GIBIBYTE;
factor *= ZBX_KIBIBYTE;