001:       SUBROUTINE SLARUV( ISEED, N, X )
002: *
003: *  -- LAPACK auxiliary routine (version 3.2) --
004: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
005: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
006: *     November 2006
007: *
008: *     .. Scalar Arguments ..
009:       INTEGER            N
010: *     ..
011: *     .. Array Arguments ..
012:       INTEGER            ISEED( 4 )
013:       REAL               X( N )
014: *     ..
015: *
016: *  Purpose
017: *  =======
018: *
019: *  SLARUV returns a vector of n random real numbers from a uniform (0,1)
020: *  distribution (n <= 128).
021: *
022: *  This is an auxiliary routine called by SLARNV and CLARNV.
023: *
024: *  Arguments
025: *  =========
026: *
027: *  ISEED   (input/output) INTEGER array, dimension (4)
028: *          On entry, the seed of the random number generator; the array
029: *          elements must be between 0 and 4095, and ISEED(4) must be
030: *          odd.
031: *          On exit, the seed is updated.
032: *
033: *  N       (input) INTEGER
034: *          The number of random numbers to be generated. N <= 128.
035: *
036: *  X       (output) REAL array, dimension (N)
037: *          The generated random numbers.
038: *
039: *  Further Details
040: *  ===============
041: *
042: *  This routine uses a multiplicative congruential method with modulus
043: *  2**48 and multiplier 33952834046453 (see G.S.Fishman,
044: *  'Multiplicative congruential random number generators with modulus
045: *  2**b: an exhaustive analysis for b = 32 and a partial analysis for
046: *  b = 48', Math. Comp. 189, pp 331-344, 1990).
047: *
048: *  48-bit integers are stored in 4 integer array elements with 12 bits
049: *  per element. Hence the routine is portable across machines with
050: *  integers of 32 bits or more.
051: *
052: *  =====================================================================
053: *
054: *     .. Parameters ..
055:       REAL               ONE
056:       PARAMETER          ( ONE = 1.0E0 )
057:       INTEGER            LV, IPW2
058:       REAL               R
059:       PARAMETER          ( LV = 128, IPW2 = 4096, R = ONE / IPW2 )
060: *     ..
061: *     .. Local Scalars ..
062:       INTEGER            I, I1, I2, I3, I4, IT1, IT2, IT3, IT4, J
063: *     ..
064: *     .. Local Arrays ..
065:       INTEGER            MM( LV, 4 )
066: *     ..
067: *     .. Intrinsic Functions ..
068:       INTRINSIC          MIN, MOD, REAL
069: *     ..
070: *     .. Data statements ..
071:       DATA               ( MM( 1, J ), J = 1, 4 ) / 494, 322, 2508,
072:      $                   2549 /
073:       DATA               ( MM( 2, J ), J = 1, 4 ) / 2637, 789, 3754,
074:      $                   1145 /
075:       DATA               ( MM( 3, J ), J = 1, 4 ) / 255, 1440, 1766,
076:      $                   2253 /
077:       DATA               ( MM( 4, J ), J = 1, 4 ) / 2008, 752, 3572,
078:      $                   305 /
079:       DATA               ( MM( 5, J ), J = 1, 4 ) / 1253, 2859, 2893,
080:      $                   3301 /
081:       DATA               ( MM( 6, J ), J = 1, 4 ) / 3344, 123, 307,
082:      $                   1065 /
083:       DATA               ( MM( 7, J ), J = 1, 4 ) / 4084, 1848, 1297,
084:      $                   3133 /
085:       DATA               ( MM( 8, J ), J = 1, 4 ) / 1739, 643, 3966,
086:      $                   2913 /
087:       DATA               ( MM( 9, J ), J = 1, 4 ) / 3143, 2405, 758,
088:      $                   3285 /
089:       DATA               ( MM( 10, J ), J = 1, 4 ) / 3468, 2638, 2598,
090:      $                   1241 /
091:       DATA               ( MM( 11, J ), J = 1, 4 ) / 688, 2344, 3406,
092:      $                   1197 /
093:       DATA               ( MM( 12, J ), J = 1, 4 ) / 1657, 46, 2922,
094:      $                   3729 /
095:       DATA               ( MM( 13, J ), J = 1, 4 ) / 1238, 3814, 1038,
096:      $                   2501 /
097:       DATA               ( MM( 14, J ), J = 1, 4 ) / 3166, 913, 2934,
098:      $                   1673 /
099:       DATA               ( MM( 15, J ), J = 1, 4 ) / 1292, 3649, 2091,
100:      $                   541 /
101:       DATA               ( MM( 16, J ), J = 1, 4 ) / 3422, 339, 2451,
102:      $                   2753 /
103:       DATA               ( MM( 17, J ), J = 1, 4 ) / 1270, 3808, 1580,
104:      $                   949 /
105:       DATA               ( MM( 18, J ), J = 1, 4 ) / 2016, 822, 1958,
106:      $                   2361 /
107:       DATA               ( MM( 19, J ), J = 1, 4 ) / 154, 2832, 2055,
108:      $                   1165 /
109:       DATA               ( MM( 20, J ), J = 1, 4 ) / 2862, 3078, 1507,
110:      $                   4081 /
111:       DATA               ( MM( 21, J ), J = 1, 4 ) / 697, 3633, 1078,
112:      $                   2725 /
113:       DATA               ( MM( 22, J ), J = 1, 4 ) / 1706, 2970, 3273,
114:      $                   3305 /
115:       DATA               ( MM( 23, J ), J = 1, 4 ) / 491, 637, 17,
116:      $                   3069 /
117:       DATA               ( MM( 24, J ), J = 1, 4 ) / 931, 2249, 854,
118:      $                   3617 /
119:       DATA               ( MM( 25, J ), J = 1, 4 ) / 1444, 2081, 2916,
120:      $                   3733 /
121:       DATA               ( MM( 26, J ), J = 1, 4 ) / 444, 4019, 3971,
122:      $                   409 /
123:       DATA               ( MM( 27, J ), J = 1, 4 ) / 3577, 1478, 2889,
124:      $                   2157 /
125:       DATA               ( MM( 28, J ), J = 1, 4 ) / 3944, 242, 3831,
126:      $                   1361 /
127:       DATA               ( MM( 29, J ), J = 1, 4 ) / 2184, 481, 2621,
128:      $                   3973 /
129:       DATA               ( MM( 30, J ), J = 1, 4 ) / 1661, 2075, 1541,
130:      $                   1865 /
131:       DATA               ( MM( 31, J ), J = 1, 4 ) / 3482, 4058, 893,
132:      $                   2525 /
133:       DATA               ( MM( 32, J ), J = 1, 4 ) / 657, 622, 736,
134:      $                   1409 /
135:       DATA               ( MM( 33, J ), J = 1, 4 ) / 3023, 3376, 3992,
136:      $                   3445 /
137:       DATA               ( MM( 34, J ), J = 1, 4 ) / 3618, 812, 787,
138:      $                   3577 /
139:       DATA               ( MM( 35, J ), J = 1, 4 ) / 1267, 234, 2125,
140:      $                   77 /
141:       DATA               ( MM( 36, J ), J = 1, 4 ) / 1828, 641, 2364,
142:      $                   3761 /
143:       DATA               ( MM( 37, J ), J = 1, 4 ) / 164, 4005, 2460,
144:      $                   2149 /
145:       DATA               ( MM( 38, J ), J = 1, 4 ) / 3798, 1122, 257,
146:      $                   1449 /
147:       DATA               ( MM( 39, J ), J = 1, 4 ) / 3087, 3135, 1574,
148:      $                   3005 /
149:       DATA               ( MM( 40, J ), J = 1, 4 ) / 2400, 2640, 3912,
150:      $                   225 /
151:       DATA               ( MM( 41, J ), J = 1, 4 ) / 2870, 2302, 1216,
152:      $                   85 /
153:       DATA               ( MM( 42, J ), J = 1, 4 ) / 3876, 40, 3248,
154:      $                   3673 /
155:       DATA               ( MM( 43, J ), J = 1, 4 ) / 1905, 1832, 3401,
156:      $                   3117 /
157:       DATA               ( MM( 44, J ), J = 1, 4 ) / 1593, 2247, 2124,
158:      $                   3089 /
159:       DATA               ( MM( 45, J ), J = 1, 4 ) / 1797, 2034, 2762,
160:      $                   1349 /
161:       DATA               ( MM( 46, J ), J = 1, 4 ) / 1234, 2637, 149,
162:      $                   2057 /
163:       DATA               ( MM( 47, J ), J = 1, 4 ) / 3460, 1287, 2245,
164:      $                   413 /
165:       DATA               ( MM( 48, J ), J = 1, 4 ) / 328, 1691, 166,
166:      $                   65 /
167:       DATA               ( MM( 49, J ), J = 1, 4 ) / 2861, 496, 466,
168:      $                   1845 /
169:       DATA               ( MM( 50, J ), J = 1, 4 ) / 1950, 1597, 4018,
170:      $                   697 /
171:       DATA               ( MM( 51, J ), J = 1, 4 ) / 617, 2394, 1399,
172:      $                   3085 /
173:       DATA               ( MM( 52, J ), J = 1, 4 ) / 2070, 2584, 190,
174:      $                   3441 /
175:       DATA               ( MM( 53, J ), J = 1, 4 ) / 3331, 1843, 2879,
176:      $                   1573 /
177:       DATA               ( MM( 54, J ), J = 1, 4 ) / 769, 336, 153,
178:      $                   3689 /
179:       DATA               ( MM( 55, J ), J = 1, 4 ) / 1558, 1472, 2320,
180:      $                   2941 /
181:       DATA               ( MM( 56, J ), J = 1, 4 ) / 2412, 2407, 18,
182:      $                   929 /
183:       DATA               ( MM( 57, J ), J = 1, 4 ) / 2800, 433, 712,
184:      $                   533 /
185:       DATA               ( MM( 58, J ), J = 1, 4 ) / 189, 2096, 2159,
186:      $                   2841 /
187:       DATA               ( MM( 59, J ), J = 1, 4 ) / 287, 1761, 2318,
188:      $                   4077 /
189:       DATA               ( MM( 60, J ), J = 1, 4 ) / 2045, 2810, 2091,
190:      $                   721 /
191:       DATA               ( MM( 61, J ), J = 1, 4 ) / 1227, 566, 3443,
192:      $                   2821 /
193:       DATA               ( MM( 62, J ), J = 1, 4 ) / 2838, 442, 1510,
194:      $                   2249 /
195:       DATA               ( MM( 63, J ), J = 1, 4 ) / 209, 41, 449,
196:      $                   2397 /
197:       DATA               ( MM( 64, J ), J = 1, 4 ) / 2770, 1238, 1956,
198:      $                   2817 /
199:       DATA               ( MM( 65, J ), J = 1, 4 ) / 3654, 1086, 2201,
200:      $                   245 /
201:       DATA               ( MM( 66, J ), J = 1, 4 ) / 3993, 603, 3137,
202:      $                   1913 /
203:       DATA               ( MM( 67, J ), J = 1, 4 ) / 192, 840, 3399,
204:      $                   1997 /
205:       DATA               ( MM( 68, J ), J = 1, 4 ) / 2253, 3168, 1321,
206:      $                   3121 /
207:       DATA               ( MM( 69, J ), J = 1, 4 ) / 3491, 1499, 2271,
208:      $                   997 /
209:       DATA               ( MM( 70, J ), J = 1, 4 ) / 2889, 1084, 3667,
210:      $                   1833 /
211:       DATA               ( MM( 71, J ), J = 1, 4 ) / 2857, 3438, 2703,
212:      $                   2877 /
213:       DATA               ( MM( 72, J ), J = 1, 4 ) / 2094, 2408, 629,
214:      $                   1633 /
215:       DATA               ( MM( 73, J ), J = 1, 4 ) / 1818, 1589, 2365,
216:      $                   981 /
217:       DATA               ( MM( 74, J ), J = 1, 4 ) / 688, 2391, 2431,
218:      $                   2009 /
219:       DATA               ( MM( 75, J ), J = 1, 4 ) / 1407, 288, 1113,
220:      $                   941 /
221:       DATA               ( MM( 76, J ), J = 1, 4 ) / 634, 26, 3922,
222:      $                   2449 /
223:       DATA               ( MM( 77, J ), J = 1, 4 ) / 3231, 512, 2554,
224:      $                   197 /
225:       DATA               ( MM( 78, J ), J = 1, 4 ) / 815, 1456, 184,
226:      $                   2441 /
227:       DATA               ( MM( 79, J ), J = 1, 4 ) / 3524, 171, 2099,
228:      $                   285 /
229:       DATA               ( MM( 80, J ), J = 1, 4 ) / 1914, 1677, 3228,
230:      $                   1473 /
231:       DATA               ( MM( 81, J ), J = 1, 4 ) / 516, 2657, 4012,
232:      $                   2741 /
233:       DATA               ( MM( 82, J ), J = 1, 4 ) / 164, 2270, 1921,
234:      $                   3129 /
235:       DATA               ( MM( 83, J ), J = 1, 4 ) / 303, 2587, 3452,
236:      $                   909 /
237:       DATA               ( MM( 84, J ), J = 1, 4 ) / 2144, 2961, 3901,
238:      $                   2801 /
239:       DATA               ( MM( 85, J ), J = 1, 4 ) / 3480, 1970, 572,
240:      $                   421 /
241:       DATA               ( MM( 86, J ), J = 1, 4 ) / 119, 1817, 3309,
242:      $                   4073 /
243:       DATA               ( MM( 87, J ), J = 1, 4 ) / 3357, 676, 3171,
244:      $                   2813 /
245:       DATA               ( MM( 88, J ), J = 1, 4 ) / 837, 1410, 817,
246:      $                   2337 /
247:       DATA               ( MM( 89, J ), J = 1, 4 ) / 2826, 3723, 3039,
248:      $                   1429 /
249:       DATA               ( MM( 90, J ), J = 1, 4 ) / 2332, 2803, 1696,
250:      $                   1177 /
251:       DATA               ( MM( 91, J ), J = 1, 4 ) / 2089, 3185, 1256,
252:      $                   1901 /
253:       DATA               ( MM( 92, J ), J = 1, 4 ) / 3780, 184, 3715,
254:      $                   81 /
255:       DATA               ( MM( 93, J ), J = 1, 4 ) / 1700, 663, 2077,
256:      $                   1669 /
257:       DATA               ( MM( 94, J ), J = 1, 4 ) / 3712, 499, 3019,
258:      $                   2633 /
259:       DATA               ( MM( 95, J ), J = 1, 4 ) / 150, 3784, 1497,
260:      $                   2269 /
261:       DATA               ( MM( 96, J ), J = 1, 4 ) / 2000, 1631, 1101,
262:      $                   129 /
263:       DATA               ( MM( 97, J ), J = 1, 4 ) / 3375, 1925, 717,
264:      $                   1141 /
265:       DATA               ( MM( 98, J ), J = 1, 4 ) / 1621, 3912, 51,
266:      $                   249 /
267:       DATA               ( MM( 99, J ), J = 1, 4 ) / 3090, 1398, 981,
268:      $                   3917 /
269:       DATA               ( MM( 100, J ), J = 1, 4 ) / 3765, 1349, 1978,
270:      $                   2481 /
271:       DATA               ( MM( 101, J ), J = 1, 4 ) / 1149, 1441, 1813,
272:      $                   3941 /
273:       DATA               ( MM( 102, J ), J = 1, 4 ) / 3146, 2224, 3881,
274:      $                   2217 /
275:       DATA               ( MM( 103, J ), J = 1, 4 ) / 33, 2411, 76,
276:      $                   2749 /
277:       DATA               ( MM( 104, J ), J = 1, 4 ) / 3082, 1907, 3846,
278:      $                   3041 /
279:       DATA               ( MM( 105, J ), J = 1, 4 ) / 2741, 3192, 3694,
280:      $                   1877 /
281:       DATA               ( MM( 106, J ), J = 1, 4 ) / 359, 2786, 1682,
282:      $                   345 /
283:       DATA               ( MM( 107, J ), J = 1, 4 ) / 3316, 382, 124,
284:      $                   2861 /
285:       DATA               ( MM( 108, J ), J = 1, 4 ) / 1749, 37, 1660,
286:      $                   1809 /
287:       DATA               ( MM( 109, J ), J = 1, 4 ) / 185, 759, 3997,
288:      $                   3141 /
289:       DATA               ( MM( 110, J ), J = 1, 4 ) / 2784, 2948, 479,
290:      $                   2825 /
291:       DATA               ( MM( 111, J ), J = 1, 4 ) / 2202, 1862, 1141,
292:      $                   157 /
293:       DATA               ( MM( 112, J ), J = 1, 4 ) / 2199, 3802, 886,
294:      $                   2881 /
295:       DATA               ( MM( 113, J ), J = 1, 4 ) / 1364, 2423, 3514,
296:      $                   3637 /
297:       DATA               ( MM( 114, J ), J = 1, 4 ) / 1244, 2051, 1301,
298:      $                   1465 /
299:       DATA               ( MM( 115, J ), J = 1, 4 ) / 2020, 2295, 3604,
300:      $                   2829 /
301:       DATA               ( MM( 116, J ), J = 1, 4 ) / 3160, 1332, 1888,
302:      $                   2161 /
303:       DATA               ( MM( 117, J ), J = 1, 4 ) / 2785, 1832, 1836,
304:      $                   3365 /
305:       DATA               ( MM( 118, J ), J = 1, 4 ) / 2772, 2405, 1990,
306:      $                   361 /
307:       DATA               ( MM( 119, J ), J = 1, 4 ) / 1217, 3638, 2058,
308:      $                   2685 /
309:       DATA               ( MM( 120, J ), J = 1, 4 ) / 1822, 3661, 692,
310:      $                   3745 /
311:       DATA               ( MM( 121, J ), J = 1, 4 ) / 1245, 327, 1194,
312:      $                   2325 /
313:       DATA               ( MM( 122, J ), J = 1, 4 ) / 2252, 3660, 20,
314:      $                   3609 /
315:       DATA               ( MM( 123, J ), J = 1, 4 ) / 3904, 716, 3285,
316:      $                   3821 /
317:       DATA               ( MM( 124, J ), J = 1, 4 ) / 2774, 1842, 2046,
318:      $                   3537 /
319:       DATA               ( MM( 125, J ), J = 1, 4 ) / 997, 3987, 2107,
320:      $                   517 /
321:       DATA               ( MM( 126, J ), J = 1, 4 ) / 2573, 1368, 3508,
322:      $                   3017 /
323:       DATA               ( MM( 127, J ), J = 1, 4 ) / 1148, 1848, 3525,
324:      $                   2141 /
325:       DATA               ( MM( 128, J ), J = 1, 4 ) / 545, 2366, 3801,
326:      $                   1537 /
327: *     ..
328: *     .. Executable Statements ..
329: *
330:       I1 = ISEED( 1 )
331:       I2 = ISEED( 2 )
332:       I3 = ISEED( 3 )
333:       I4 = ISEED( 4 )
334: *
335:       DO 10 I = 1, MIN( N, LV )
336: *
337:   20     CONTINUE
338: *
339: *        Multiply the seed by i-th power of the multiplier modulo 2**48
340: *
341:          IT4 = I4*MM( I, 4 )
342:          IT3 = IT4 / IPW2
343:          IT4 = IT4 - IPW2*IT3
344:          IT3 = IT3 + I3*MM( I, 4 ) + I4*MM( I, 3 )
345:          IT2 = IT3 / IPW2
346:          IT3 = IT3 - IPW2*IT2
347:          IT2 = IT2 + I2*MM( I, 4 ) + I3*MM( I, 3 ) + I4*MM( I, 2 )
348:          IT1 = IT2 / IPW2
349:          IT2 = IT2 - IPW2*IT1
350:          IT1 = IT1 + I1*MM( I, 4 ) + I2*MM( I, 3 ) + I3*MM( I, 2 ) +
351:      $         I4*MM( I, 1 )
352:          IT1 = MOD( IT1, IPW2 )
353: *
354: *        Convert 48-bit integer to a real number in the interval (0,1)
355: *
356:          X( I ) = R*( REAL( IT1 )+R*( REAL( IT2 )+R*( REAL( IT3 )+R*
357:      $            REAL( IT4 ) ) ) )
358: *         
359:          IF (X( I ).EQ.1.0) THEN
360: *           If a real number has n bits of precision, and the first
361: *           n bits of the 48-bit integer above happen to be all 1 (which
362: *           will occur about once every 2**n calls), then X( I ) will
363: *           be rounded to exactly 1.0. In IEEE single precision arithmetic,
364: *           this will happen relatively often since n = 24.
365: *           Since X( I ) is not supposed to return exactly 0.0 or 1.0,
366: *           the statistically correct thing to do in this situation is
367: *           simply to iterate again.
368: *           N.B. the case X( I ) = 0.0 should not be possible.  
369:             I1 = I1 + 2
370:             I2 = I2 + 2
371:             I3 = I3 + 2
372:             I4 = I4 + 2
373:             GOTO 20
374:          END IF
375: *
376:    10 CONTINUE
377: *
378: *     Return final value of seed
379: *
380:       ISEED( 1 ) = IT1
381:       ISEED( 2 ) = IT2
382:       ISEED( 3 ) = IT3
383:       ISEED( 4 ) = IT4
384:       RETURN
385: *
386: *     End of SLARUV
387: *
388:       END
389: