From 1f564d729b147fb79831008af820a018f500a73a Mon Sep 17 00:00:00 2001
From: Guillaume Horel <guillaume.horel@gmail.com>
Date: Sat, 31 Oct 2020 10:00:48 -0400
Subject: [PATCH] fix avx2 detection

reword commits to make it clearer
---
 cpuid_x86.c             | 16 ++++++++--------
 driver/others/dynamic.c | 12 ++++++------
 2 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/cpuid_x86.c b/cpuid_x86.c
index 728d459d1..84c12ff43 100644
--- a/cpuid_x86.c
+++ b/cpuid_x86.c
@@ -202,7 +202,7 @@ int support_avx(){
   if ((ecx & (1 << 28)) != 0 && (ecx & (1 << 27)) != 0 && (ecx & (1 << 26)) != 0){
     xgetbv(0, &eax, &edx);
     if((eax & 6) == 6){
-      ret=1;  //OS support AVX
+      ret=1;  //OS supports saving xmm and ymm registers (6 = (1<<1) | (1<<2))
     }
   }
   return ret;
@@ -219,8 +219,8 @@ int support_avx2(){
   if (!support_avx()) 
     return 0;
   cpuid(7, &eax, &ebx, &ecx, &edx);
-  if((ebx & (1<<7)) != 0)
-      ret=1;  //OS supports AVX2
+  if((ebx & (1<<5)) != 0)
+      ret=1;  //CPU supports AVX2
   return ret;
 #else
   return 0;
@@ -235,14 +235,14 @@ int support_avx512(){
   if (!support_avx()) 
     return 0;
   cpuid(7, &eax, &ebx, &ecx, &edx);
-  if((ebx & 32) != 32){
-      ret=0;  //OS does not even support AVX2
+  if((ebx & (1<<5)) == 0){
+      ret=0;  //cpu does not have avx2 flag
   }
-  if((ebx & (1<<31)) != 0){
+  if((ebx & (1<<31)) != 0){ //AVX512VL flag
     xgetbv(0, &eax, &edx); 
     if((eax & 0xe0) == 0xe0)
-      ret=1;  //OS supports AVX512VL
-  }
+      ret=1;  //OS supports saving zmm registers
+ }
   return ret;
 #else
   return 0;
diff --git a/driver/others/dynamic.c b/driver/others/dynamic.c
index 21d2c7948..58f4d8b59 100644
--- a/driver/others/dynamic.c
+++ b/driver/others/dynamic.c
@@ -330,8 +330,8 @@ int support_avx2(){
   if (!support_avx())
     return 0;
   cpuid(7, &eax, &ebx, &ecx, &edx);
-  if((ebx & (1<<7)) != 0)
-      ret=1;  //OS supports AVX2
+  if((ebx & (1<<5)) != 0)
+      ret=1;  //AVX2 flag is set
   return ret;
 #else
   return 0;
@@ -346,13 +346,13 @@ int support_avx512(){
   if (!support_avx())
     return 0;
   cpuid(7, &eax, &ebx, &ecx, &edx);
-  if((ebx & (1<<7)) == 0){
-      ret=0;  //OS does not even support AVX2
+  if((ebx & (1<<5)) == 0){
+      ret=0;  //cpu does not have avx2 flag
   }
-  if((ebx & (1u<<31)) != 0){
+  if((ebx & (1<<31)) != 0){ //AVX512VL flag is set
     xgetbv(0, &eax, &edx);
     if((eax & 0xe0) == 0xe0)
-      ret=1;  //OS supports AVX512VL
+      ret=1;  //OS supports saving zmm register
   }
   return ret;
 #else