SQUOZE: Difference between revisions

This article is about a compression scheme. For the similarly named transponder code in aeronautics, see Squawk code.

SQUOZE (abbreviated as SQZ) is a memory-efficient representation of a combined source and relocatable object program file with a symbol table on punched cards which was introduced in 1958 with the SCAT assembler on the SHARE Operating System (SOS) for the IBM 709. A program in this format was called a SQUOZE deck. It was also used on later machines including the IBM 7090 and 7094.

Encoding

In the SQUOZE encoding, identifiers in the symbol table were represented in a 50-character alphabet, allowing a 36-bit machine word to represent six alphanumeric characters plus two flag bits, thus saving two bits per six characters, because the six bits normally allocated for each character could store up to 64 states rather than only the 50 states needed to represent the 50 letters of the alphabet, and 50⁶ < 2³⁴.

SQUOZE character codes

Most significant digits			Least significant digits
		Dec	+0	+1	+2	+3	+4	+5	+6	+7
		Oct	0	1	2	3	4	5	6	7
Dec	Oct	Bin	000	001	010	011	100	101	110	111
+0	0	000	space	0	1	2	3	4	5	6
+8	1	001	7	8	9	A	B	C	D	E
+16	2	010	F	G	H	I	J	K	L	M
+24	3	011	N	O	P	Q	R	S	T	U
+32	4	100	V	W	X	Y	Z	= #	/ %	) ⌑
+40	5	101	+ &	-	- @	+ &	-	*	/	$
+48	6	110	,	.	—	—	—	—	—	—

Using base 50 already saves a single bit every three characters, so it was used in two three-character chunks. The manual has a formula for encoding six characters ABCDEF: $(A*50^{2}+B*50+C)*2^{17}+(D*50^{2}+E*50+F)$

For example "SQUOZE", normally 36 bits: 35 33 37 31 44 17_{(base 8)} would be encoded in two 17-bit pieces to fit in the 34 bits as ( 0o220231 << 17 ) | 0o175473 == 0o110114575473.

A simpler example of the same logic would be how a three-digit BCD number would take up 12 bits, such as 987: 9 8 7_{(base 16)} 1001 1000 0111_{(base 2)}, but any such value could be stored in 10 bits directly, saving two bits, such as 987: 3db_{(base 16)} 11 1101 1011_{(base 2)}.

Etymology

"Squoze" is a facetious past participle of the verb 'to squeeze'.

The name SQUOZE was later borrowed for similar schemes used on DEC machines; they had a 40-character alphabet (50 in octal) and were called DEC RADIX 50 and MOD40, but sometimes nicknamed DEC Squoze.

See also

• Packed BCD
• Hertz encoding
• Chen–Ho encoding
• Densely packed decimal (DPD)
• BCD (character encoding)
• Base 50 (numeral system)
• Base conversion

Further reading

• Williams, Al (2016-11-22). "Squoze your data". Hackaday. Archived from the original on 2020-06-06. Retrieved 2020-06-06.
• Ehrman, John Robert; Snyder, James N. (1964-04-15). "3.3.2.1 SCAT". The PORTHOS Executive System for the IBM 7094 - User's Manual (PDF). University of Illinois, Graduate College Digital Computer Laboratory. Archived (PDF) from the original on 2020-06-07. Retrieved 2020-06-07. […] SCAT is a two part assembler which in brief operates as follows: Programs written symbolically as one order per card are ingested during the first phase by the "compiler" which scans the program for symbols and outputs a condensed deck of cards (SQUOZE deck) containing tables of these symbols and the program condensed and efficiently coded. During the second phase this SQUOZE deck is ingested by the "modify and load" program which converts the object program to binary machine language which by option can either be loaded ready to run or output on absolute binary cards (23 orders per card) for loading and running at a later time. The "lister" can produce a printed version of the program at either of these stages. Symbolic corrections to a program can be inserted into the second phase along with the SQUOZE deck. […] (1 page)