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Re: adding numbers and floating point errors

by imp (Priest)
on Nov 22, 2006 at 21:42 UTC ( #585618=note: print w/ replies, xml ) Need Help??


in reply to adding numbers and floating point errors

BrowserUK provided an excellent explanation for why this occurs a few years ago.

To (mostly) fix the issue for your script you can use bignum.

use bignum; my $c = 0; for ($x = 0; $x <= 4; $x += 0.05){ $c++; print "[$c] x= $x (".sprintf("%20.40f",$x).") \n"; }
[1] x= 0 (0.0000000000000000000000000000000000000000) [2] x= 0.05 (0.0500000000000000027755575615628913510591) [3] x= 0.1 (0.1000000000000000055511151231257827021182) [4] x= 0.15 (0.1499999999999999944488848768742172978818) [5] x= 0.2 (0.2000000000000000111022302462515654042363) [6] x= 0.25 (0.2500000000000000000000000000000000000000) [7] x= 0.3 (0.2999999999999999888977697537484345957637) [8] x= 0.35 (0.3499999999999999777955395074968691915274) [9] x= 0.4 (0.4000000000000000222044604925031308084726) [10] x= 0.45 (0.4500000000000000111022302462515654042363) [11] x= 0.5 (0.5000000000000000000000000000000000000000) [12] x= 0.55 (0.5500000000000000444089209850062616169453) [13] x= 0.6 (0.5999999999999999777955395074968691915274) [14] x= 0.65 (0.6500000000000000222044604925031308084726) [15] x= 0.7 (0.6999999999999999555910790149937383830547) [16] x= 0.75 (0.7500000000000000000000000000000000000000) [17] x= 0.8 (0.8000000000000000444089209850062616169453) [18] x= 0.85 (0.8499999999999999777955395074968691915274) [19] x= 0.9 (0.9000000000000000222044604925031308084726) [20] x= 0.95 (0.9499999999999999555910790149937383830547) [21] x= 1 (1.0000000000000000000000000000000000000000) [22] x= 1.05 (1.0500000000000000444089209850062616169453) [23] x= 1.1 (1.1000000000000000888178419700125232338905) [24] x= 1.15 (1.1499999999999999111821580299874767661095) [25] x= 1.2 (1.1999999999999999555910790149937383830547) [26] x= 1.25 (1.2500000000000000000000000000000000000000) [27] x= 1.3 (1.3000000000000000444089209850062616169453) [28] x= 1.35 (1.3500000000000000888178419700125232338905) [29] x= 1.4 (1.3999999999999999111821580299874767661095) [30] x= 1.45 (1.4499999999999999555910790149937383830547) [31] x= 1.5 (1.5000000000000000000000000000000000000000) [32] x= 1.55 (1.5500000000000000444089209850062616169453) [33] x= 1.6 (1.6000000000000000888178419700125232338905) [34] x= 1.65 (1.6499999999999999111821580299874767661095) [35] x= 1.7 (1.6999999999999999555910790149937383830547) [36] x= 1.75 (1.7500000000000000000000000000000000000000) [37] x= 1.8 (1.8000000000000000444089209850062616169453) [38] x= 1.85 (1.8500000000000000888178419700125232338905) [39] x= 1.9 (1.8999999999999999111821580299874767661095) [40] x= 1.95 (1.9499999999999999555910790149937383830547) [41] x= 2 (2.0000000000000000000000000000000000000000) [42] x= 2.05 (2.0499999999999998223643160599749535322189) [43] x= 2.1 (2.1000000000000000888178419700125232338905) [44] x= 2.15 (2.1499999999999999111821580299874767661095) [45] x= 2.2 (2.2000000000000001776356839400250464677811) [46] x= 2.25 (2.2500000000000000000000000000000000000000) [47] x= 2.3 (2.2999999999999998223643160599749535322189) [48] x= 2.35 (2.3500000000000000888178419700125232338905) [49] x= 2.4 (2.3999999999999999111821580299874767661095) [50] x= 2.45 (2.4500000000000001776356839400250464677811) [51] x= 2.5 (2.5000000000000000000000000000000000000000) [52] x= 2.55 (2.5499999999999998223643160599749535322189) [53] x= 2.6 (2.6000000000000000888178419700125232338905) [54] x= 2.65 (2.6499999999999999111821580299874767661095) [55] x= 2.7 (2.7000000000000001776356839400250464677811) [56] x= 2.75 (2.7500000000000000000000000000000000000000) [57] x= 2.8 (2.7999999999999998223643160599749535322189) [58] x= 2.85 (2.8500000000000000888178419700125232338905) [59] x= 2.9 (2.8999999999999999111821580299874767661095) [60] x= 2.95 (2.9500000000000001776356839400250464677811) [61] x= 3 (3.0000000000000000000000000000000000000000) [62] x= 3.05 (3.0499999999999998223643160599749535322189) [63] x= 3.1 (3.1000000000000000888178419700125232338905) [64] x= 3.15 (3.1499999999999999111821580299874767661095) [65] x= 3.2 (3.2000000000000001776356839400250464677811) [66] x= 3.25 (3.2500000000000000000000000000000000000000) [67] x= 3.3 (3.2999999999999998223643160599749535322189) [68] x= 3.35 (3.3500000000000000888178419700125232338905) [69] x= 3.4 (3.3999999999999999111821580299874767661095) [70] x= 3.45 (3.4500000000000001776356839400250464677811) [71] x= 3.5 (3.5000000000000000000000000000000000000000) [72] x= 3.55 (3.5499999999999998223643160599749535322189) [73] x= 3.6 (3.6000000000000000888178419700125232338905) [74] x= 3.65 (3.6499999999999999111821580299874767661095) [75] x= 3.7 (3.7000000000000001776356839400250464677811) [76] x= 3.75 (3.7500000000000000000000000000000000000000) [77] x= 3.8 (3.7999999999999998223643160599749535322189)
[78] x= 3.85 (3.8500000000000000888178419700125232338905) [79] x= 3.9 (3.8999999999999999111821580299874767661095) [80] x= 3.95 (3.9500000000000001776356839400250464677811) [81] x= 4 (4.0000000000000000000000000000000000000000)


Comment on Re: adding numbers and floating point errors
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Re^2: adding numbers and floating point errors
by smeenz (Sexton) on Nov 22, 2006 at 21:56 UTC
    Thanks. That explanation does indeed explain the issue.

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