Avoid negation of signed integers in C that may hold INT*_MIN.

Reported by minoki.
Recent C compilers 'take advantage' of the undefined behavior.
This completely changes the meaning of expressions like (k == -k).

1 files changed, 4 insertions, 4 deletions

diff --git a/src/lj_vmmath.c b/src/lj_vmmath.c
index ff41ba28..6369bc6b 100644
--- a/src/lj_vmmath.c
+++ b/src/lj_vmmath.c
@@ -66,11 +66,11 @@ int32_t LJ_FASTCALL lj_vm_modi(int32_t a, int32_t b)
 {
   uint32_t y, ua, ub;
   lua_assert(b != 0);  /* This must be checked before using this function. */
-  ua = a < 0 ? (uint32_t)-a : (uint32_t)a;
-  ub = b < 0 ? (uint32_t)-b : (uint32_t)b;
+  ua = a < 0 ? ~(uint32_t)a+1u : (uint32_t)a;
+  ub = b < 0 ? ~(uint32_t)b+1u : (uint32_t)b;
   y = ua % ub;
   if (y != 0 && (a^b) < 0) y = y - ub;
-  if (((int32_t)y^b) < 0) y = (uint32_t)-(int32_t)y;
+  if (((int32_t)y^b) < 0) y = ~y+1u;
   return (int32_t)y;
 }
 #endif
@@ -105,7 +105,7 @@ double lj_vm_powi(double x, int32_t k)
   else if (k == 0)
     return 1.0;
   else
-    return 1.0 / lj_vm_powui(x, (uint32_t)-k);
+    return 1.0 / lj_vm_powui(x, ~(uint32_t)k+1u);
 }
 
 /* Computes fpm(x) for extended math functions. */