产生一个更大的随机数的方法

//////////////////////////////////////////////////////////////////////////
// Function: f_BigRand
//
// Description:
// This function uses 2 calls to Rand to generate Random numbers for large
// ranges. It breaks the range into blocks of 32767 (max range for
// RAND function)
// The limit of the function is 32767 blocks of 32767. 
// It calls RAND to first determine which block, then calls RAND again to 
// determine the number in the
// selected block. To ensure even probability over the range where
// there are multiple blocks,
// the same sub range is used for each block.
// 
// Argument al_range 
// The upper limit of the range of random numbers you want returned.
// The lower limit is always 1. The maximum value for the argument is 
// 1,073,676,289 or 32767*32767.
// 
// Returns
// A random number in the range 1 to al_range inclusive.
// Or 0 if max range exceeded.
//
// Author: David Dennis
//////////////////////////////////////////////////////////////////////////
//
// Revision History
// 
// -----------------------------------------------------------------------
// VERSION CHANGE ID WHO WHEN WHAT/WHY
// -----------------------------------------------------------------------
// 6.30 8/4/00 Initial version.
//////////////////////////////////////////////////////////////////////////
Long ll_Offset, ll_Return
Integer li_Range, li_Blocks

// Block size is set to 32767 as this is the maximum range
// the RAND function can handle 
Integer li_BlockSize = 32767

IF al_range > 1073676289 THEN
//Range is too big
Return 0
END IF

//Determine The number of blocks
li_Blocks = Truncate(al_range/li_BlockSize,0) 

//Add an extra block to accommodate any remainder
IF Mod(al_range, li_BlockSize) > 0 THEN
li_Blocks = li_Blocks + 1
END IF

// Improve efficiency for ranges less than Block Size
// where there is only one block 
IF al_range < li_BlockSize THEN
li_Range = al_range
ELSE
li_Range = li_BlockSize
END IF

ll_Return = 0

// Loop until the value is in range. 
// If the value is not in range, calculate the 
// Offset again to ensure even probability 
DO UNTIL (ll_Return > 0) And (ll_Return <= al_Range)
// Calculate a Random Offset using the number
// of blocks as the range. 
// Offsets will range from [0 to (li_Blocks - 1)*BlockSize]
// in increments of BlockSize
ll_Offset = (Rand(li_Blocks) - 1) * li_BlockSize

//Main Calculation
ll_Return = ll_Offset + Rand(li_Range)
LOOP

Return ll_Return