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Possible bug: f128 constant only has 16 decimals of precision when printed #3612

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bdezonia opened this issue Nov 6, 2019 · 2 comments · Fixed by #19229
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Possible bug: f128 constant only has 16 decimals of precision when printed #3612

bdezonia opened this issue Nov 6, 2019 · 2 comments · Fixed by #19229
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bug Observed behavior contradicts documented or intended behavior contributor friendly This issue is limited in scope and/or knowledge of Zig internals. standard library This issue involves writing Zig code for the standard library.
Milestone
0.12.0

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@bdezonia
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bdezonia commented Nov 6, 2019

Using 0.5.0 the following code:

var z : f128 = 1.738954882048422195749048390299;
warn("{:.34}\n",z);

Shows this:

1.7389548820484222000000000000000000e+00

It's like the compile time constant is 64 bit rather than 128 bit. The documentation implies that floating constants are 128 bit.

Is this a bug? Or am I doing something wrong?
@andrewrk andrewrk added this to the 0.7.0 milestone Nov 14, 2019
@andrewrk andrewrk added bug Observed behavior contradicts documented or intended behavior contributor friendly This issue is limited in scope and/or knowledge of Zig internals. standard library This issue involves writing Zig code for the standard library. labels Nov 14, 2019
@LakeByTheWoods
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This is because the current float formatter internally works on 64bit floats. #1299 should fix this.

@Mouvedia
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dupe of #1181?

@andrewrk andrewrk modified the milestones: 0.7.0, 0.8.0 Oct 30, 2020
@andrewrk andrewrk modified the milestones: 0.8.0, 0.9.0 Nov 6, 2020
@andrewrk andrewrk modified the milestones: 0.9.0, 0.10.0 May 19, 2021
@tiehuis tiehuis mentioned this issue Mar 9, 2024
Merged
@andrewrk andrewrk modified the milestones: 0.15.0, 0.12.0 Mar 12, 2024
RossComputerGuy pushed a commit to ExpidusOS/zig that referenced this issue Mar 20, 2024
@tiehuis @RossComputerGuy
std.fmt: add ryu floating-point formatting
eedcf56 
This replaces the errol backend with one based on ryu. The 128-bit
backend only is implemented. This supports all floating-point types and
does not use fp logic to print.

Closes ziglang#1181.
Closes ziglang#1299.
Closes ziglang#3612.
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bug Observed behavior contradicts documented or intended behavior contributor friendly This issue is limited in scope and/or knowledge of Zig internals. standard library This issue involves writing Zig code for the standard library.
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std.fmt: add ryu floating-point formatting implementation tiehuis/zig
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@andrewrk @Mouvedia @bdezonia @LakeByTheWoods