Editing Addressing mode (section)

===Indirect to bit field within word===
Some computers had special indirect addressing modes for subfields within words.

The [[GE-600 series|GE/Honeywell 600 series]] character addressing indirect word specified either 6-bit or 9-bit character fields within its [[36-bit computing|36-bit]] word.

The DEC [[PDP-10]], also 36-bit, had special instructions which allowed memory to be treated as a sequence of fixed-size bit fields or bytes of any size from 1 bit to 36 bits. A one-word sequence descriptor in memory, called a "byte pointer", held the current word address within the sequence, a bit position within a word, and the size of each byte.

Instructions existed to load and store bytes via this descriptor, and to increment the descriptor to point at the next byte (bytes were not split across word boundaries). Much DEC software used five 7-bit bytes per word (plain ASCII characters), with one bit per word unused. Implementations of [[C (programming language)|C]] had to use four 9-bit bytes per word, since the 'malloc' function in C assumes that the size of an ''int'' is some multiple of the size of a ''char'';<ref>[http://www.codingunit.com/c-reference-stdlib-h-function-malloc "C Reference: function malloc()"]</ref> the actual multiple is determined by the system-dependent compile-time operator [[sizeof]].