slaruv/dlaruv: fix seed advancement on rejected uniform deviate#1288
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jschueller wants to merge 1 commit into
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slaruv/dlaruv: fix seed advancement on rejected uniform deviate#1288jschueller wants to merge 1 commit into
jschueller wants to merge 1 commit into
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When the computed random value rounds to exactly 1.0 (once every
~2^24 single-precision calls), both SLARAN and SLARUV reject it and
recompute — but they advanced the seed differently:
SLARAN: ISEED(1:4) = IT1..IT4 (correct — carry forward the
multiplier-transformed state)
SLARUV: I1 = I1 + 2 (wrong — ad-hoc skip in seed
space)
SLARUV's +2 produces a different subsequent random sequence than
SLARAN would for the same initial seed. Fix by using the same
seed advancement in both: set I1..I4 = IT1..IT4, matching SLARAN.
Applies to DLARUV as well.
Closes Reference-LAPACK#1108
martin-frbg
approved these changes
Jun 11, 2026
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When the computed random value rounds to exactly 1.0 (once every ~2^24 single-precision calls), both SLARAN and SLARUV reject it and recompute — but they advanced the seed differently:
SLARAN: ISEED(1:4) = IT1..IT4 (correct — carry forward the
multiplier-transformed state)
SLARUV: I1 = I1 + 2 (wrong — ad-hoc skip in seed
space)
SLARUV's +2 produces a different subsequent random sequence than SLARAN would for the same initial seed. Fix by using the same seed advancement in both: set I1..I4 = IT1..IT4, matching SLARAN.
Applies to DLARUV as well.
Closes #1108