utilasm.h

/*
 * utilasm.h
 *
 * This file provides optional inline-assembly helpers for low-level bit
 * manipulation on supported x86/x64 targets. These macros are used to map a
 * few performance-sensitive operations, such as shifting, testing, setting,
 * and clearing bits, to specific machine instructions when inline assembly is
 * enabled.
 *
 * The intent is to centralize these architecture-specific primitives behind a
 * small interface so the rest of the codebase can use them conditionally while
 * keeping the generic implementation paths separate.
 */

#ifndef INCLUDE_UTILASM_H_
#define INCLUDE_UTILASM_H_

#include <roaring/portability.h>

#ifdef __cplusplus
extern "C" {
namespace roaring {
#endif

#if defined(CROARING_INLINE_ASM)
#define CROARING_ASMBITMANIPOPTIMIZATION  // optimization flag

#define CROARING_ASM_SHIFT_RIGHT(srcReg, bitsReg, destReg) \
    __asm volatile("shrx %1, %2, %0"                       \
                   : "=r"(destReg)                         \
                   :             /* write */               \
                   "r"(bitsReg), /* read only */           \
                   "r"(srcReg)   /* read only */           \
    )

#define CROARING_ASM_INPLACESHIFT_RIGHT(srcReg, bitsReg) \
    __asm volatile("shrx %1, %0, %0"                     \
                   : "+r"(srcReg)                        \
                   :            /* read/write */         \
                   "r"(bitsReg) /* read only */          \
    )

#define CROARING_ASM_SHIFT_LEFT(srcReg, bitsReg, destReg) \
    __asm volatile("shlx %1, %2, %0"                      \
                   : "=r"(destReg)                        \
                   :             /* write */              \
                   "r"(bitsReg), /* read only */          \
                   "r"(srcReg)   /* read only */          \
    )
// set bit at position testBit within testByte to 1 and
// copy cmovDst to cmovSrc if that bit was previously clear
#define CROARING_ASM_SET_BIT_INC_WAS_CLEAR(testByte, testBit, count) \
    __asm volatile(                                                  \
        "bts %2, %0\n"                                               \
        "sbb $-1, %1\n"                                              \
        : "+r"(testByte), /* read/write */                           \
          "+r"(count)                                                \
        :            /* read/write */                                \
        "r"(testBit) /* read only */                                 \
    )

#define CROARING_ASM_CLEAR_BIT_DEC_WAS_SET(testByte, testBit, count) \
    __asm volatile(                                                  \
        "btr %2, %0\n"                                               \
        "sbb $0, %1\n"                                               \
        : "+r"(testByte), /* read/write */                           \
          "+r"(count)                                                \
        :            /* read/write */                                \
        "r"(testBit) /* read only */                                 \
    )

#define CROARING_ASM_BT64(testByte, testBit, count) \
    __asm volatile(                                 \
        "bt %2,%1\n"                                \
        "sbb %0,%0" /*could use setb */             \
        : "=r"(count)                               \
        :              /* write */                  \
        "r"(testByte), /* read only */              \
        "r"(testBit)   /* read only */              \
    )

#endif

#ifdef __cplusplus
}
}  // extern "C" { namespace roaring {
#endif

#endif /* INCLUDE_UTILASM_H_ */