[Lldb-commits] [lldb] r346783 - [Cocoa] Implement formatter for the new NSDate representation.

[Zachary Turner via lldb-commits]

On Tue, Nov 13, 2018 at 11:46 AM Davide Italiano via lldb-commits <
lldb-commits at lists.llvm.org> wrote:

> Author: davide
> Date: Tue Nov 13 11:43:43 2018
> New Revision: 346783
>
> URL: http://llvm.org/viewvc/llvm-project?rev=346783&view=rev
> Log:
> [Cocoa] Implement formatter for the new NSDate representation.
>
> <rdar://problem/46002786>
>
> Modified:
>     lldb/trunk/source/Plugins/Language/ObjC/Cocoa.cpp
>
> Modified: lldb/trunk/source/Plugins/Language/ObjC/Cocoa.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/lldb/trunk/source/Plugins/Language/ObjC/Cocoa.cpp?rev=346783&r1=346782&r2=346783&view=diff
>
> ==============================================================================
> --- lldb/trunk/source/Plugins/Language/ObjC/Cocoa.cpp (original)
> +++ lldb/trunk/source/Plugins/Language/ObjC/Cocoa.cpp Tue Nov 13 11:43:43
> 2018
> @@ -742,6 +742,60 @@ bool lldb_private::formatters::NSURLSumm
>    return false;
>  }
>
> +/// Bias value for tagged pointer exponents.
> +/// Recommended values:
> +/// 0x3e3: encodes all dates between distantPast and distantFuture
> +///   except for the range within about 1e-28 second of the reference
> date.
> +/// 0x3ef: encodes all dates for a few million years beyond distantPast
> and
> +///   distantFuture, except within about 1e-25 second of the reference
> date.
> +const int TAGGED_DATE_EXPONENT_BIAS = 0x3ef;
> +
> +typedef union {
> +  struct {
> +    uint64_t fraction:52;  // unsigned
> +    uint64_t exponent:11;  // signed
> +    uint64_t sign:1;
> +  };
> +  uint64_t i;
> +  double d;
> +} DoubleBits;
> +typedef union {
> +  struct {
> +    uint64_t fraction:52;  // unsigned
> +    uint64_t exponent:7;   // signed
> +    uint64_t sign:1;
> +    uint64_t unused:4;  // placeholder for pointer tag bits
> +  };
>
MSVC gives:

warning C4201: nonstandard extension used: nameless struct/union


> +  uint64_t i;
> +} TaggedDoubleBits;
> +
> +static uint64_t decodeExponent(uint64_t exp) {
> +  int64_t exp7 = exp;
> +  // Tagged exponent field is 7-bit signed. Sign-extend the value to 64
> bits
> +  // before performing arithmetic.
> +  int64_t exp11 = ((exp7 << 57) >> 57) + TAGGED_DATE_EXPONENT_BIAS;
> +  return exp11;
> +}
>
this should probably be:

return llvm::SignExtend64<7>(exp) + TAGGED_DATE_EXPONENT_BIAS;


> +
> +static uint64_t decodeTaggedTimeInterval(uint64_t encodedTimeInterval) {
> +  if (encodedTimeInterval == 0)
> +    return 0.0;
> +  if (encodedTimeInterval == std::numeric_limits<uint64_t>::max())
> +    return -0.0;
> +
> +  TaggedDoubleBits encodedBits = { .i = encodedTimeInterval };
>
Designated initializers are C++20 which are not allowed in LLVM.
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