Query on mapping kCFNumberCharType to kCFNumberSInt8Type

Gayathri_Bhaskaran · 2016-10-27T10:26:50.000Z

Hello

As per

apple/swift-corelibs-foundation/blob/main/CoreFoundation/NumberDate.subproj/CFNumber.c#L432


      
          };
          static const CFNumberRef kCFNumberFloat64Zero = &__kCFNumberFloat64Zero;
          
          
static _CF_CONSTANT_OBJECT_BACKING struct __CFNumber __kCFNumberFloat64One = {
              INIT_CFRUNTIME_BASE_WITH_CLASS_AND_FLAGS(__NSCFNumber, _kCFRuntimeIDCFNumber, kCFNumberFloat64CanonicalTypeIndex),
              { ._64.floatValue = 1.0f }
          };
          static const CFNumberRef kCFNumberFloat64One = &__kCFNumberFloat64One;
          
          
static const struct {
              uint16_t canonicalType:5;	// canonical fixed-width type
              uint16_t floatBit:1;	// is float
              uint16_t storageBit:1;	// storage size (0: (float ? 4 : 8), 1: (float ? 8 : 16) bits)
              uint16_t lgByteSize:3;	// base-2 log byte size of public type
              uint16_t unused:6;
          } __CFNumberTypeTable[] = {
              /* 0 */			{0, 0, 0, 0},
          
          
    /* kCFNumberSInt8Type */	{kCFNumberSInt8Type, 0, 0, 0, 0},
              /* kCFNumberSInt16Type */	{kCFNumberSInt16Type, 0, 0, 1, 0},
              /* kCFNumberSInt32Type */	{kCFNumberSInt32Type, 0, 0, 2, 0},

It is observed that kCFNumberCharType is mapped to kCFNumberSInt8Type. Is
there any reason why kCFNumberCharType is mapped to kCFNumberSInt8Type ?

Does it make sense to map kCFNumberCharType to kCFNumberCharType itself ?
Any inputs on this is appreciated.

Regards
Gayathri Bhaskaran

Tony_Parker · 2016-10-27T16:10:27.000Z

Hi Gayathri,

The first entry in that table is the “canonical fixed width type”. We want char to be 8 bits, so we use the SInt8 there. If you look at the places where we use the canonical type it expects it to be one of a more limited set of values.

- Tony

···

On Oct 27, 2016, at 3:26 AM, Gayathri Bhaskaran via swift-corelibs-dev <swift-corelibs-dev@swift.org> wrote:

Hello

As per https://github.com/apple/swift-corelibs-foundation/blob/master/CoreFoundation/NumberDate.subproj/CFNumber.c#L432

It is observed that kCFNumberCharType is mapped to kCFNumberSInt8Type. Is there any reason why kCFNumberCharType is mapped to kCFNumberSInt8Type ?

Does it make sense to map kCFNumberCharType to kCFNumberCharType itself ? Any inputs on this is appreciated.

Regards
Gayathri Bhaskaran

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