C++ 动态新闻推送 第9期

int main() {
  using std::literals::string_view_literals::operator""sv;
  std::cout << "trade.price"sv.contains("order"); // prints 0
  std::cout << "trade.price"sv.contains("");      // prints 1
  std::cout << "trade.price"sv.contains("price"); // prints 1
}

std::sort(my_vector.begin(), my_vector.end(),
    [](std::string const& lhs, std::string const& rhs) {
        return lhs.size() < rhs.size();
    });

std::sort(my_vector.begin(), my_vector.end(),
    [] TL(_1.size() < _2.size());
    });

#include <stdint.h>
#include <stddef.h>
#include <string.h>

typedef void *upb_msg;
struct upb_decstate;
typedef struct upb_decstate upb_decstate;

// The standard set of arguments passed to each parsing function.
// Thanks to x86-64 calling conventions, these will be passed in registers.
#define UPB_PARSE_PARAMS                                          \
  upb_decstate *d, const char *ptr, upb_msg *msg, intptr_t table, \
      uint64_t hasbits, uint64_t data
#define UPB_PARSE_ARGS d, ptr, msg, table, hasbits, data

#define UNLIKELY(x) __builtin_expect(x, 0)
#define MUSTTAIL __attribute__((musttail))

const char *fallback(UPB_PARSE_PARAMS);
const char *dispatch(UPB_PARSE_PARAMS);

// Code to parse a 4-byte fixed field that uses a 1-byte tag (field 1-15).
const char *upb_pf32_1bt(UPB_PARSE_PARAMS) {
  // Decode "data", which contains information about this field.
  uint8_t hasbit_index = data >> 24;
  size_t ofs = data >> 48;

  if (UNLIKELY(data & 0xff)) {
    // Wire type mismatch (the dispatch function xor's the expected wire type
    // with the actual wire type, so data & 0xff == 0 indicates a match).
    MUSTTAIL return fallback(UPB_PARSE_ARGS);
  }

  ptr += 1;  // Advance past tag.

  // Store data to message.
  hasbits |= 1ull << hasbit_index;
  memcpy((char*)msg + ofs, ptr, 4);

  ptr += 4;  // Advance past data.

  // Call dispatch function, which will read the next tag and branch to the
  // correct field parser function.
  MUSTTAIL return dispatch(UPB_PARSE_ARGS);
}

upb_pf32_1bt:                           # @upb_pf32_1bt
        mov     rax, r9
        shr     rax, 24
        bts     r8, rax
        test    r9b, r9b
        jne     .LBB0_1
        mov     r10, r9
        shr     r10, 48
        mov     eax, dword ptr [rsi + 1]
        mov     dword ptr [rdx + r10], eax
        add     rsi, 5
        jmp     dispatch                        # TAILCALL
.LBB0_1:
        jmp     fallback                        # TAILCALL

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