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@ -9,7 +9,7 @@ |
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.\" of any kind. I shall in no event be liable for anything that happens |
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.\" to anyone/anything when using this software. |
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.\" |
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.\" $OpenBSD: rand48.3,v 1.6 1999/09/27 02:00:13 aaron Exp $ |
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.\" $OpenBSD: rand48.3,v 1.7 2000/04/20 13:50:02 aaron Exp $ |
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.\" |
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.Dd October 8, 1993 |
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.Dt RAND48 3 |
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@ -49,12 +49,13 @@ |
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The |
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.Fn rand48 |
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family of functions generates pseudo-random numbers using a linear |
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congruential algorithm working on integers 48 bits in size. The |
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particular formula employed is |
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congruential algorithm working on integers 48 bits in size. |
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The particular formula employed is |
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r(n+1) = (a * r(n) + c) mod m |
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where the default values are |
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for the multiplicand a = 0xfdeece66d = 25214903917 and |
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the addend c = 0xb = 11. The modulus is always fixed at m = 2 ** 48. |
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the addend c = 0xb = 11. |
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The modulus is always fixed at m = 2 ** 48. |
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r(n) is called the seed of the random number generator. |
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.Pp |
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For all the six generator routines described next, the first |
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@ -63,7 +64,8 @@ computational step is to perform a single iteration of the algorithm. |
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.Fn drand48 |
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and |
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.Fn erand48 |
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return values of type double. The full 48 bits of r(n+1) are |
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return values of type double. |
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The full 48 bits of r(n+1) are |
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loaded into the mantissa of the returned value, with the exponent set |
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such that the values produced lie in the interval [0.0, 1.0). |
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.Pp |
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@ -71,7 +73,8 @@ such that the values produced lie in the interval [0.0, 1.0). |
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and |
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.Fn nrand48 |
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return values of type long in the range |
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[0, 2**31-1]. The high-order (31) bits of |
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[0, 2**31-1]. |
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The high-order (31) bits of |
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r(n+1) are loaded into the lower bits of the returned value, with |
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the topmost (sign) bit set to zero. |
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.Pp |
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@ -79,14 +82,15 @@ the topmost (sign) bit set to zero. |
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and |
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.Fn jrand48 |
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return values of type long in the range |
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[-2**31, 2**31-1]. The high-order (32) bits of |
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r(n+1) are loaded into the returned value. |
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[-2**31, 2**31-1]. |
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The high-order (32) bits of r(n+1) are loaded into the returned value. |
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.Pp |
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.Fn drand48 , |
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.Fn lrand48 , |
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and |
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.Fn mrand48 |
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use an internal buffer to store r(n). For these functions |
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use an internal buffer to store r(n). |
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For these functions |
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the initial value of r(0) = 0x1234abcd330e = 20017429951246. |
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.Pp |
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On the other hand, |
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@ -118,8 +122,8 @@ also initializes the internal buffer r(n) of |
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and |
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.Fn mrand48 , |
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but here all 48 bits of the seed can be specified in an array of 3 shorts, |
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where the zeroth member specifies the lowest bits. Again, |
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the constant multiplicand and addend of the algorithm are |
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where the zeroth member specifies the lowest bits. |
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Again, the constant multiplicand and addend of the algorithm are |
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reset to the default values given above. |
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.Fn seed48 |
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returns a pointer to an array of 3 shorts which contains the old seed. |
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aaron
24 years ago