在高级向量扩展 (AVX) 中,比较指令如_m256_cmp_ps,最后一个参数是比较谓词。谓词的选择让我不知所措。它们似乎是类型、排序、信号的三重奏。例如,_CMP_LE_OS 是“小于或等于”的有序信号。
对于初学者来说,选择信令或非信令是否有性能原因,并且类似地,有序或无序比另一个更快?
“无信号”甚至是什么意思?我在文档中根本找不到这个。关于何时选择什么的任何经验法则?
以下是来自 avxintrin.h 的谓词选择:
/* Compare */
#define _CMP_EQ_OQ 0x00 /* Equal (ordered, non-signaling) */
#define _CMP_LT_OS 0x01 /* Less-than (ordered, signaling) */
#define _CMP_LE_OS 0x02 /* Less-than-or-equal (ordered, signaling) */
#define _CMP_UNORD_Q 0x03 /* Unordered (non-signaling) */
#define _CMP_NEQ_UQ 0x04 /* Not-equal (unordered, non-signaling) */
#define _CMP_NLT_US 0x05 /* Not-less-than (unordered, signaling) */
#define _CMP_NLE_US 0x06 /* Not-less-than-or-equal (unordered, signaling) */
#define _CMP_ORD_Q 0x07 /* Ordered (nonsignaling) */
#define _CMP_EQ_UQ 0x08 /* Equal (unordered, non-signaling) */
#define _CMP_NGE_US 0x09 /* Not-greater-than-or-equal (unord, signaling) */
#define _CMP_NGT_US 0x0a /* Not-greater-than (unordered, signaling) */
#define _CMP_FALSE_OQ 0x0b /* False (ordered, non-signaling) */
#define _CMP_NEQ_OQ 0x0c /* Not-equal (ordered, non-signaling) */
#define _CMP_GE_OS 0x0d /* Greater-than-or-equal (ordered, signaling) */
#define _CMP_GT_OS 0x0e /* Greater-than (ordered, signaling) */
#define _CMP_TRUE_UQ 0x0f /* True (unordered, non-signaling) */
#define _CMP_EQ_OS 0x10 /* Equal (ordered, signaling) */
#define _CMP_LT_OQ 0x11 /* Less-than (ordered, non-signaling) */
#define _CMP_LE_OQ 0x12 /* Less-than-or-equal (ordered, non-signaling) */
#define _CMP_UNORD_S 0x13 /* Unordered (signaling) */
#define _CMP_NEQ_US 0x14 /* Not-equal (unordered, signaling) */
#define _CMP_NLT_UQ 0x15 /* Not-less-than (unordered, non-signaling) */
#define _CMP_NLE_UQ 0x16 /* Not-less-than-or-equal (unord, non-signaling) */
#define _CMP_ORD_S 0x17 /* Ordered (signaling) */
#define _CMP_EQ_US 0x18 /* Equal (unordered, signaling) */
#define _CMP_NGE_UQ 0x19 /* Not-greater-than-or-equal (unord, non-sign) */
#define _CMP_NGT_UQ 0x1a /* Not-greater-than (unordered, non-signaling) */
#define _CMP_FALSE_OS 0x1b /* False (ordered, signaling) */
#define _CMP_NEQ_OS 0x1c /* Not-equal (ordered, signaling) */
#define _CMP_GE_OQ 0x1d /* Greater-than-or-equal (ordered, non-signaling) */
#define _CMP_GT_OQ 0x1e /* Greater-than (ordered, non-signaling) */
#define _CMP_TRUE_US 0x1f /* True (unordered, signaling) */