initial commit

1 files changed, 95 insertions, 0 deletions

diff --git a/inlineasm.h b/inlineasm.h
new file mode 100644
index 0000000..af466d3
--- /dev/null
+++ b/inlineasm.h
@@ -0,0 +1,95 @@
+#include <stdint.h>
+
+#if defined(__i386__)
+
+//averages at about 80 ticks with an offset of 1
+static uint32_t optmemmeasure(char* memory, uint32_t offset)
+{
+    asm(
+        "rdtsc ;"
+        "mov %%eax, %%ebp ;"
+
+        "cmpb $0x23, (%%ebx) ;"
+        "cmpb $0x42, (%%ebx, %%ecx) ;"
+
+        "rdtsc ;"
+        "sub %%ebp, %%eax ;"
+        : : "b" (memory), "c" (offset)
+       );
+}
+
+static uint64_t rdtsc()
+{
+    uint64_t rdtsc;
+
+    asm(
+        "rdtsc ;"
+        : "=A" (rdtsc)
+       );
+    
+    return rdtsc;
+}
+
+#elif defined(__x86_64__)
+
+// this implementation uses all of the data provided by rdtsc but uses
+// more instrucions
+// averages at about 77.3 ticks with an offset of 1
+static uint64_t memmeasure(char* memory, uint64_t offset)
+{
+    asm(
+        "rdtsc ;"
+        "shl $32, %%rdx ;"
+        "add %%rax, %%rdx ;"
+        "mov %%rdx, %%rdi ;"
+        
+        // here be magic dragons and memory access (read segfaults) ahead
+        // TODO: evaluate if more cmp types (like w and l) do make sense 
+        "cmpb $0x23, (%%rbx) ;"
+        "cmpb $0x42, (%%rbx,%%rcx) ;"
+        
+        "rdtsc ;"
+        "shl $32, %%rdx ;"
+        "add %%rdx, %%rax ;"
+        "sub %%rdi, %%rax ;" //result in rax with is the return value
+        : : "b" (memory), "c" (offset)
+       );
+}
+ 
+// this implementation only uses the lower part of the values retured by
+// rdtsc to save instrucions. it is not significantly faster than the
+// accurate one but it has fewer instrucions and by that is less likely
+// to be delayed by the scheduler
+// averages at about 72.5 ticks with an offset of 1
+static uint64_t  optmemmeasure(char* memory, uint64_t offset)
+{
+    asm(
+        "rdtsc ;"
+        "mov %%eax, %%edi ;"
+        
+        // here be magic dragons and memory access (read segfaults) ahead
+        // TODO: evaluate if more cmp types (like w and l) do make sense 
+        "cmpb $0x23, (%%rbx) ;"
+        "cmpb $0x42, (%%rbx,%%rcx) ;"
+        
+        "rdtsc ;"
+        "sub %%edi, %%eax ;"
+        : : "b" (memory), "c" (offset)
+       );
+}
+
+// smal implentation to get the rdtsc counter
+static uint64_t rdtsc()
+{
+    asm(
+        "rdtsc ;"
+        "shl $32, %rdx ;"
+        "add %rdx, %rax"
+       );
+}
+
+#else
+
+#error "This code only supports x86 and x86_64"
+
+#endif