Home » Archimedes archive » Acorn User » AU 1997-10 A.adf » Extras » Apple][e/PD/BOB/ARMBOB/!ArmBob/progs/h/power
Apple][e/PD/BOB/ARMBOB/!ArmBob/progs/h/power
This website contains an archive of files for the Acorn Electron, BBC Micro, Acorn Archimedes, Commodore 16 and Commodore 64 computers, which Dominic Ford has rescued from his private collection of floppy disks and cassettes.
Some of these files were originally commercial releases in the 1980s and 1990s, but they are now widely available online. I assume that copyright over them is no longer being asserted. If you own the copyright and would like files to be removed, please contact me.
| Tape/disk: | Home » Archimedes archive » Acorn User » AU 1997-10 A.adf » Extras |
| Filename: | Apple][e/PD/BOB/ARMBOB/!ArmBob/progs/h/power |
| Read OK: | ✔ |
| File size: | 034F bytes |
| Load address: | 0000 |
| Exec address: | 0000 |
File contents
/* exponentiate GCW 12/01/95
power(x,y) defined if
# y is a positive integer
# y is a negative integer and x is a nonzero real
# y is a real and x is a positive real
result has same type as x.
*/
power(x,y)
{
switch (typeof(y))
{
case REAL:
if (x < 0.0) quit("Positive real argument needed");
else return (x > 0.0)?(exp(y*log(x))):0.0;
break;
case INTEGER:
switch (typeof(x))
{
case REAL:
return (y < 0)?fastpower(1.0/x,-y):fastpower(x,y);
break;
case INTEGER:
if (y < 0) quit("Positive exponent needed");
else return fastpower(x,y);
break;
}
break;
}
}
fastpower(x,y)
{
if (y == 0) return (typeof(x) == REAL)?1.0:1;
if (y == 1) return x;
if (y%2) return x*fastpower(x*x,y/2);
else return fastpower(x*x, y/2);
}
00000000 2f 2a 20 65 78 70 6f 6e 65 6e 74 69 61 74 65 20 |/* exponentiate |
00000010 20 20 20 20 20 20 20 47 43 57 20 20 31 32 2f 30 | GCW 12/0|
00000020 31 2f 39 35 0a 0a 20 20 20 70 6f 77 65 72 28 78 |1/95.. power(x|
00000030 2c 79 29 20 64 65 66 69 6e 65 64 20 69 66 0a 20 |,y) defined if. |
00000040 20 20 20 20 20 20 23 20 20 79 20 69 73 20 61 20 | # y is a |
00000050 70 6f 73 69 74 69 76 65 20 69 6e 74 65 67 65 72 |positive integer|
00000060 0a 20 20 20 20 20 20 20 23 20 20 79 20 69 73 20 |. # y is |
00000070 61 20 6e 65 67 61 74 69 76 65 20 69 6e 74 65 67 |a negative integ|
00000080 65 72 20 61 6e 64 20 78 20 69 73 20 61 20 6e 6f |er and x is a no|
00000090 6e 7a 65 72 6f 20 72 65 61 6c 0a 20 20 20 20 20 |nzero real. |
000000a0 20 20 23 20 20 79 20 69 73 20 61 20 72 65 61 6c | # y is a real|
000000b0 20 61 6e 64 20 78 20 69 73 20 61 20 70 6f 73 69 | and x is a posi|
000000c0 74 69 76 65 20 72 65 61 6c 0a 20 20 20 72 65 73 |tive real. res|
000000d0 75 6c 74 20 68 61 73 20 73 61 6d 65 20 74 79 70 |ult has same typ|
000000e0 65 20 61 73 20 78 2e 0a 2a 2f 0a 0a 70 6f 77 65 |e as x..*/..powe|
000000f0 72 28 78 2c 79 29 0a 7b 0a 20 73 77 69 74 63 68 |r(x,y).{. switch|
00000100 20 28 74 79 70 65 6f 66 28 79 29 29 0a 20 7b 0a | (typeof(y)). {.|
00000110 20 20 63 61 73 65 20 52 45 41 4c 3a 0a 20 20 20 | case REAL:. |
00000120 20 69 66 20 28 78 20 3c 20 30 2e 30 29 20 71 75 | if (x < 0.0) qu|
00000130 69 74 28 22 50 6f 73 69 74 69 76 65 20 72 65 61 |it("Positive rea|
00000140 6c 20 61 72 67 75 6d 65 6e 74 20 6e 65 65 64 65 |l argument neede|
00000150 64 22 29 3b 0a 20 20 20 20 65 6c 73 65 20 72 65 |d");. else re|
00000160 74 75 72 6e 20 28 78 20 3e 20 30 2e 30 29 3f 28 |turn (x > 0.0)?(|
00000170 65 78 70 28 79 2a 6c 6f 67 28 78 29 29 29 3a 30 |exp(y*log(x))):0|
00000180 2e 30 3b 0a 20 20 20 20 62 72 65 61 6b 3b 0a 20 |.0;. break;. |
00000190 20 63 61 73 65 20 49 4e 54 45 47 45 52 3a 0a 20 | case INTEGER:. |
000001a0 20 20 20 73 77 69 74 63 68 20 28 74 79 70 65 6f | switch (typeo|
000001b0 66 28 78 29 29 0a 20 20 20 20 7b 0a 20 20 20 20 |f(x)). {. |
000001c0 20 63 61 73 65 20 52 45 41 4c 3a 0a 20 20 20 20 | case REAL:. |
000001d0 20 20 20 20 72 65 74 75 72 6e 20 28 79 20 3c 20 | return (y < |
000001e0 30 29 3f 66 61 73 74 70 6f 77 65 72 28 31 2e 30 |0)?fastpower(1.0|
000001f0 2f 78 2c 2d 79 29 3a 66 61 73 74 70 6f 77 65 72 |/x,-y):fastpower|
00000200 28 78 2c 79 29 3b 0a 20 20 20 20 20 20 20 20 62 |(x,y);. b|
00000210 72 65 61 6b 3b 0a 20 20 20 20 20 63 61 73 65 20 |reak;. case |
00000220 49 4e 54 45 47 45 52 3a 0a 20 20 20 20 20 20 20 |INTEGER:. |
00000230 20 69 66 20 28 79 20 3c 20 30 29 20 71 75 69 74 | if (y < 0) quit|
00000240 28 22 50 6f 73 69 74 69 76 65 20 65 78 70 6f 6e |("Positive expon|
00000250 65 6e 74 20 6e 65 65 64 65 64 22 29 3b 0a 20 20 |ent needed");. |
00000260 20 20 20 20 20 20 65 6c 73 65 20 72 65 74 75 72 | else retur|
00000270 6e 20 66 61 73 74 70 6f 77 65 72 28 78 2c 79 29 |n fastpower(x,y)|
00000280 3b 0a 20 20 20 20 20 20 20 20 62 72 65 61 6b 3b |;. break;|
00000290 0a 20 20 20 20 20 7d 0a 20 20 20 20 20 62 72 65 |. }. bre|
000002a0 61 6b 3b 0a 20 7d 0a 7d 0a 0a 66 61 73 74 70 6f |ak;. }.}..fastpo|
000002b0 77 65 72 28 78 2c 79 29 0a 7b 0a 20 69 66 20 28 |wer(x,y).{. if (|
000002c0 79 20 3d 3d 20 30 29 20 72 65 74 75 72 6e 20 28 |y == 0) return (|
000002d0 74 79 70 65 6f 66 28 78 29 20 3d 3d 20 52 45 41 |typeof(x) == REA|
000002e0 4c 29 3f 31 2e 30 3a 31 3b 0a 20 69 66 20 28 79 |L)?1.0:1;. if (y|
000002f0 20 3d 3d 20 31 29 20 72 65 74 75 72 6e 20 78 3b | == 1) return x;|
00000300 0a 20 69 66 20 28 79 25 32 29 20 72 65 74 75 72 |. if (y%2) retur|
00000310 6e 20 78 2a 66 61 73 74 70 6f 77 65 72 28 78 2a |n x*fastpower(x*|
00000320 78 2c 79 2f 32 29 3b 0a 20 65 6c 73 65 20 72 65 |x,y/2);. else re|
00000330 74 75 72 6e 20 66 61 73 74 70 6f 77 65 72 28 78 |turn fastpower(x|
00000340 2a 78 2c 20 79 2f 32 29 3b 0a 7d 0a 20 20 20 |*x, y/2);.}. |
0000034f 
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