Import PSTR and pgm_read_float fixes

Fixes #3

Also removes register keyword which is going away in later C++ versions
from the macro.  It was always a hint, and the C compiler was free to
ignore it anyway.  GCC should still be smart enough to use registers
when possible.

Author: earlephilhower

newlib/libc/sys/xtensa/sys/pgmspace.h

@@ -34,7 +34,9 @@ extern "C" {
 // PSTR() macro modified to start on a 32-bit boundary.  This adds on average
 // 1.5 bytes/string, but in return memcpy_P and strcpy_P will work 4~8x faster
 #ifndef PSTR
-  #define PSTR(s)            (__extension__({static const char __c[] __attribute__((__aligned__(4))) PROGMEM = (s); &__c[0];}))
+    // Adapted from AVR-specific code at https://forum.arduino.cc/index.php?topic=194603.0
+    // Uses C attribute section instead of ASM block to allow for C language string concatenation ("x" "y" === "xy")
+    #define PSTR(s) (__extension__({static const char __c[] __attribute__((__aligned__(4))) __attribute__((section( "\".irom0.pstr." __FILE__ "." __STRINGIZE(__LINE__) "."  __STRINGIZE(__COUNTER__) "\", \"aSM\", @progbits, 1 #"))) = (s); &__c[0];}))
 #endif
 
 // Flash memory must be read using 32 bit aligned addresses else a processor
@@ -66,18 +68,26 @@ extern "C" {
       :"a15");
 
 static inline uint8_t pgm_read_byte_inlined(const void* addr) {
-  register uint32_t res;
+  uint32_t res;
   pgm_read_with_offset(addr, res);
   return (uint8_t) res;     /* This masks the lower byte from the returned word */
 }
 
 /* Although this says "word", it's actually 16 bit, i.e. half word on Xtensa */
 static inline uint16_t pgm_read_word_inlined(const void* addr) {
-  register uint32_t res;
+  uint32_t res;
   pgm_read_with_offset(addr, res);
   return (uint16_t) res;    /* This masks the lower half-word from the returned word */
 }
 
+/* Can't legally cast bits of uint32_t to a float w/o conversion or std::memcpy, which is inefficient. */
+/* The ASM block doesn't care the type, so just pass in what C thinks is a float and return in custom fcn. */
+static inline float pgm_read_float_unaligned(const void *addr) {
+  float res;
+  pgm_read_with_offset(addr, res);
+  return res;
+}
+
 #define pgm_read_byte(addr)                pgm_read_byte_inlined(addr)
 #define pgm_read_word_aligned(addr)        pgm_read_word_inlined(addr)
 #ifdef __cplusplus
@@ -96,7 +106,6 @@ static inline uint32_t pgm_read_dword_unaligned(const void *addr) {
   return res;
 }
 
-#define pgm_read_float_unaligned(addr) ((float)pgm_read_dword_unaligned(addr))
 #define pgm_read_ptr_unaligned(addr)   ((void*)pgm_read_dword_unaligned(addr))
 #define pgm_read_word_unaligned(addr)  ((uint16_t)(pgm_read_dword_unaligned(addr) & 0xffff))