Remove empty state from FixedSpan #29240
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PR #29240: Size comparison from f47ce53 to 314e759 Increases (43 builds for bl702, bl702l, cc13x4_26x4, cc32xx, cyw30739, efr32, esp32, k32w, linux, mbed, psoc6, qpg)
Decreases (32 builds for bl602, bl702, bl702l, cc13x4_26x4, cc32xx, esp32, linux, psoc6)
Full report (46 builds for bl602, bl702, bl702l, cc13x4_26x4, cc32xx, cyw30739, efr32, esp32, k32w, linux, mbed, psoc6, qpg)
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PR #29240: Size comparison from d4cbdbc to 53a01ba Increases above 0.2%:
Increases (32 builds for bl602, bl702, bl702l, cc13x4_26x4, cc32xx, cyw30739, k32w, linux, mbed, nrfconnect, psoc6, qpg)
Decreases (32 builds for bl602, bl702, bl702l, cc13x4_26x4, cc32xx, cyw30739, k32w, linux, mbed, nrfconnect, psoc6, qpg)
Full report (32 builds for bl602, bl702, bl702l, cc13x4_26x4, cc32xx, cyw30739, k32w, linux, mbed, nrfconnect, psoc6, qpg)
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Prior to this change, a default-constructed FixedSpan would be in a state with empty() = true but size() > 0, but nevertheless compare as not equal to an empty non-fixed Span. After this change, a FixedSpan always contains a valid sequence of elements of the relevant size. This aligns the behavior with std::span. The IsSpanUsable() function and the empty() method have been removed because they would always return true, and hence invite programmer errors. Since we still rely on default-constructing certain FixedByteSpan types in a number of places, such instances are now initialized to point to an array of zeroes (the arrays for all sizes of span are shared and limited in size to avoid inadvertently blowing out the constant data size in the binary).
This is validated using VerifyOrDie, but only in code paths that take a raw pointer and size; code paths that take a T[] assume the array is valid and remain unchecked and constexpr.
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PR #29240: Size comparison from 6e3d045 to af697ed Increases above 0.2%:
Increases (65 builds for bl602, bl702, bl702l, cc13x4_26x4, cc32xx, cyw30739, efr32, esp32, k32w, linux, mbed, nrfconnect, psoc6, qpg, telink)
Decreases (13 builds for bl702, bl702l, cc32xx, esp32, linux, psoc6)
Full report (65 builds for bl602, bl702, bl702l, cc13x4_26x4, cc32xx, cyw30739, efr32, esp32, k32w, linux, mbed, nrfconnect, psoc6, qpg, telink)
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- Fix buffer size check in ConvertECDSASignatureRawToDER - Add deleted nullptr_t overloads to Span and FixedSpan - Comments around constexpr / VerifyOrDie
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PR #29240: Size comparison from 6e3d045 to e55e143 Increases above 0.2%:
Increases (65 builds for bl602, bl702, bl702l, cc13x4_26x4, cc32xx, cyw30739, efr32, esp32, k32w, linux, mbed, nrfconnect, psoc6, qpg, telink)
Decreases (9 builds for cc32xx, esp32, linux, psoc6)
Full report (65 builds for bl602, bl702, bl702l, cc13x4_26x4, cc32xx, cyw30739, efr32, esp32, k32w, linux, mbed, nrfconnect, psoc6, qpg, telink)
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Sep 19, 2023
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PR #29240: Size comparison from 6e3d045 to 72c3f84 Increases above 0.2%:
Increases (38 builds for bl602, bl702, bl702l, cc13x4_26x4, cc32xx, cyw30739, efr32, esp32, k32w, linux, mbed, nrfconnect, psoc6, qpg)
Decreases (29 builds for bl702, bl702l, cc13x4_26x4, cc32xx, cyw30739, efr32, esp32, k32w, linux, psoc6, qpg)
Full report (38 builds for bl602, bl702, bl702l, cc13x4_26x4, cc32xx, cyw30739, efr32, esp32, k32w, linux, mbed, nrfconnect, psoc6, qpg)
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PR #29240: Size comparison from 6fe4b11 to ae8c4ed Increases above 0.2%:
Increases (66 builds for bl602, bl702, bl702l, cc13x4_26x4, cc32xx, cyw30739, efr32, esp32, k32w, linux, mbed, nrfconnect, psoc6, qpg, telink)
Decreases (8 builds for cc32xx, esp32, linux, psoc6)
Full report (66 builds for bl602, bl702, bl702l, cc13x4_26x4, cc32xx, cyw30739, efr32, esp32, k32w, linux, mbed, nrfconnect, psoc6, qpg, telink)
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Oct 23, 2023
* Remove empty state from FixedSpan Prior to this change, a default-constructed FixedSpan would be in a state with empty() = true but size() > 0, but nevertheless compare as not equal to an empty non-fixed Span. After this change, a FixedSpan always contains a valid sequence of elements of the relevant size. This aligns the behavior with std::span. The IsSpanUsable() function and the empty() method have been removed because they would always return true, and hence invite programmer errors. Since we still rely on default-constructing certain FixedByteSpan types in a number of places, such instances are now initialized to point to an array of zeroes (the arrays for all sizes of span are shared and limited in size to avoid inadvertently blowing out the constant data size in the binary). * Disallow Spans pointing to null if size is not 0 This is validated using VerifyOrDie, but only in code paths that take a raw pointer and size; code paths that take a T[] assume the array is valid and remain unchecked and constexpr. * Deprecate IsSpanUsable(Span) in favor of !empty() * Fix test cases that use invalid ByteSpans * Use ByteSpan() for empty span instead of ByteSpan(nullptr, 0) * Address review comments - Fix buffer size check in ConvertECDSASignatureRawToDER - Add deleted nullptr_t overloads to Span and FixedSpan - Comments around constexpr / VerifyOrDie * Fix project-chip#29326 as per review --------- Co-authored-by: Andrei Litvin <andy314@gmail.com>
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Prior to this change, a default-constructed FixedSpan would be in a state
with empty() = true but size() > 0, and despite being empty compare as not
equal to an empty non-fixed Span.
After this change, a FixedSpan always contains a valid sequence of elements
of the relevant size. This aligns the behavior with std::span.
The IsSpanUsable() function and the empty() method have been removed
because they would always return true, and hence invite programmer errors.
Since we still rely on default-constructing certain FixedByteSpan types in
a number of places, such instances are now initialized to point to an array
of zeroes (the arrays for all sizes of span are shared and limited in size
to avoid inadvertently blowing out the constant data size in the binary).
Also ensure that non-fixed Spans don't point to
nullptrunlesssize == 0, anddeprecate IsSpanUsable(Span) in favor of !empty()
This means both types of Spans are always valid in the sense that in-bounds
access is safe. Only non-fixed Spans can be empty.