The TI-57 is a mid-range programmable calculator that belongs to the same family as the TI-55, and can be considered a successor of the SR-56. It was the first calculator from Texas Instruments that offered a fully merged keystroke programming model: operations that required as many as four keystrokes (e.g., INV 2nd Prd 0) now fit into a single program step. The calculator relied on label addressing for control transfer; this and some other characteristics of its programming model strongly suggests that the engineers at Texas Instruments took notice of Hewlett-Packard's programmable models.

Despite the meager size (50 steps) of its program memory, keystroke merging made the TI-57 a very versatile tool. I find the limited number of data registers a more severe constraint. Only 8 registers are available, and these are liberally used by many of the calculator's built-in functions. For instance, the t-register was mapped to register 7, precluding the simultaneous use of both; registers 6 and 5 were used for pending operations when evaluating complex expressions. These "features", for lack of a better term, made programming on the TI-57 more of a chore than it needed to be.

Despite these problems, I found it possible to cram a Gamma function program with 7-digit accuracy into the calculator's limited program memory. When entering the program, you must set the contents of registers 2-7 to the listed values (this needs to be done only once.) To enter constants that are accurate to the calculator's 10 digits of internal precision (as opposed to the 8 digits of the display) use a technique like this:

8.2784822 ÷ 10 + 68 = STO 3

.9596084 + 755 = STO 4

To use the program, enter a positive real argument and key SBR 0.

Incidentally, the length of this program makes it possible to add the two program steps necessary to put the TI-57 into "constant memory" mode, as described on the home page of Gene Wright. Briefly, you need to enter the two steps with the following keystrokes: GTO 2nd 4 8 LRN 2nd Exc SST 2nd Lbl 1. To put the calculator in sleep mode, enter CLR GTO 2nd 4 8 R/S INV STO 3 +/- +/-. To exit sleep mode enter INV 2nd Fix CLR.

M2=√2π
M3=68.82784822
M4=755.9596084
M5=4151.488796
M6=11399.36541
M7=12520.43913

00  86 0   LBL 0
01  32 0   STO 0
02  32 1   STO 1
03  33 2   RCL 2
04  39 0   PRD 0
05  33 3   RCL 3
06  34 0   SUM 0
07  33 1   RCL 1
08  39 0   PRD 0
09  33 4   RCL 4
10  34 0   SUM 0
11  33 1   RCL 1
12  39 0   PRD 0
13  33 5   RCL 5
14  34 0   SUM 0
15  33 1   RCL 1
16  39 0   PRD 0
17  33 6   RCL 6
18  34 0   SUM 0
19  33 7   RCL 7
20  45     ÷
21  33 1   RCL 1
22  85     =
23  34 0   SUM 0
24  05     5
25  38 0   EXC 0
26  86 1   LBL 1
27  45     ÷
28  01     1
29  34 1   SUM 1
30  33 1   RCL 1
31  56     DSZ
32  51 1   GTO 1
33  55     ×
34  83     .
35  05     5
36  34 1   SUM 1
37  33 1   RCL 1
38  32 0   STO 0
39  35     yx
40  05     5
41 -34 1   INV SUM 1
42  33 1   RCL 1
43  45     ÷
44  33 0   RCL 0
45 -13     INV lnx
46  85     =
47 -61     INV SBR

For some additional information about the TI-57, please see these fascinating articles contributed by Claus Buchholz:

• The TI-57 Memory Map
• TI-57 Constant ROM