eliminate warnings when compiling with -ffast-math

src/Makefile.common

@@ -102,7 +102,7 @@ else ifeq ($(BUILD), c99)
     CFLAGS += -std=c99
 else ifeq ($(BUILD), retroarch)
     # RetroArch builds with gcc8 and gnu99 which adds some extra warning validations
-    SRC_CFLAGS += -std=gnu99 -D_GNU_SOURCE -Wall -Warray-bounds=2 -Wincompatible-pointer-types
+    SRC_CFLAGS += -std=gnu99 -D_GNU_SOURCE -Wall -Warray-bounds=2 -Wincompatible-pointer-types -ffast-math
     # Also include the RC_CLIENT_SUPPORTS_EXTERNAL flag to ensure we do the full level of validation on the
     # most code. The c89 build will ensure things still build without the RC_CLIENT_SUPPORTS_EXTERNAL flag.
     CFLAGS += -DRC_CLIENT_SUPPORTS_EXTERNAL

src/api/rc_api_user.c

@@ -471,7 +471,7 @@ int rc_api_process_fetch_all_user_progress_server_response(rc_api_fetch_all_user
     entry = response->entries;
     while (rc_json_get_next_object_field(&iterator, &field))
     {
-      entry->game_id = (uint32_t)strtol(field.name, &end, 10);
+      entry->game_id = (uint32_t)strtoul(field.name, &end, 10);
 
       field.name = "";
       if (!rc_json_get_required_object(entry_fields, sizeof(entry_fields) / sizeof(entry_fields[0]),

src/libretro/rc_libretro.c

@@ -633,7 +633,7 @@ static void rc_libretro_memory_init_from_memory_map(rc_libretro_memory_regions_t
         /* if we need to extract a disconnect bit, the largest block we can read is up to
          * the next time that bit flips */
         /* https://stackoverflow.com/questions/12247186/find-the-lowest-set-bit */
-        disconnect_size = (uint32_t)(desc->disconnect & -((int)desc->disconnect));
+        disconnect_size = (uint32_t)(desc->disconnect & ((size_t)0 - desc->disconnect));
         desc_size = disconnect_size - (real_address & (disconnect_size - 1));
       }
 

src/runtime/rc_memref.c

@@ -10,6 +10,9 @@
 #include <stdlib.h> /* malloc/realloc */
 #include <string.h> /* memcpy */
 #include <math.h>   /* INFINITY/NAN */
+#include <float.h>  /* FLT_RADIX/FLT_MANT_DIG/FLT_MAX_EXP */
+
+#include <stdio.h>
 
 #define MEMREF_PLACEHOLDER_ADDRESS 0xFFFFFFFF
 
@@ -344,23 +347,27 @@ static float rc_build_float(uint32_t mantissa_bits, int32_t exponent, int sign)
   double dbl = ((double)mantissa) / ((double)implied_bit);
 
   if (exponent > 127) {
-    /* exponent above 127 is a special number */
-    if (mantissa_bits == 0) {
-      /* infinity */
-#ifdef INFINITY /* INFINITY and NAN #defines require C99 */
-      dbl = (double)INFINITY;
-#else
-      dbl = -log(0.0);
-#endif
-    }
-    else {
-      /* NaN */
-#ifdef NAN
-      dbl = NAN;
+    /* An exponent above 127 is a special number: infinity when the mantissa is zero, NaN otherwise. */
+
+#if FLT_RADIX == 2 && FLT_MANT_DIG == 24 && FLT_MAX_EXP == 128
+    /* The system is IEEE754 capable. Use a memcpy to shuffle an IEEE754 constant into the variable to
+     * avoid a warning when compiling with -ffast-math. -ffast-math optimizes out special logic for NaN
+     * and infinity to provide a small performance boost. As such, actually using the values may result
+     * in undefined behavior - hence the warning. But consumers want to be able to use that flag, so this
+     * is the easiest way to support it. */
+    const uint32_t ieee754_inf = 0x7F800000;
+    const uint32_t ieee754_nan = 0x7FC00000;
+    float f;
+    memcpy(&f, (mantissa_bits == 0) ? &ieee754_inf : &ieee754_nan, sizeof(float));
+    dbl = (double)f;
+#elif defined(INFINITY) && defined(NAN)
+    /* If we're not on an IEEE754 system, rely on the constants provided by the compiler. */
+    dbl = (double)(mantissa_bits == 0 ? INFINITY : NAN);
 #else
-      dbl = -sqrt(-1);
+    /* C89 doesn't define INFINITY or NAN. Fallback to FLT_MAX and hope all achievement logic uses full
+     * range checking as non-float data could appear as >X or <Y whereas NaN would be neither >X nor <Y */
+    dbl = (double)FLT_MAX;
 #endif
-    }
   }
   else if (exponent > 0) {
     /* exponent from 1 to 127 is a number greater than 1 */