Added to/from string conversion functions, and testcases for them.

libfixmath/fix16.h

@@ -208,6 +208,17 @@ extern fix16_t fix16_log2(fix16_t x) FIXMATH_FUNC_ATTRS;
  */
 extern fix16_t fix16_slog2(fix16_t x) FIXMATH_FUNC_ATTRS;
 
+/*! Convert fix16_t value to a string.
+ * Required buffer length for largest values is 13 bytes.
+ */
+extern void fix16_to_str(fix16_t value, char *buf, int decimals);
+
+/*! Convert string to a fix16_t value
+ * Ignores spaces at beginning and end. Returns fix16_overflow if
+ * value is too large or there were garbage characters.
+ */
+extern fix16_t fix16_from_str(const char *buf);
+
 #ifdef __cplusplus
 }
 #include "fix16.hpp"

libfixmath/fix16_str.c

@@ -0,0 +1,114 @@
+#include "fix16.h"
+#include <stdbool.h>
+#include <ctype.h>
+
+static const uint32_t scales[8] = {
+    /* 5 decimals is enough for full fix16_t precision */
+    1, 10, 100, 1000, 10000, 100000, 100000, 100000
+};
+
+static char *itoa_loop(char *buf, uint32_t scale, uint32_t value, bool skip)
+{
+    while (scale)
+    {
+        unsigned digit = (value / scale);
+    
+        if (!skip || digit || scale == 1)
+        {
+            skip = false;
+            *buf++ = '0' + digit;
+            value %= scale;
+        }
+        
+        scale /= 10;
+    }
+    return buf;
+}
+
+void fix16_to_str(fix16_t value, char *buf, int decimals)
+{
+    uint32_t uvalue = (value >= 0) ? value : -value;
+    if (value < 0)
+        *buf++ = '-';
+
+    /* Separate the integer and decimal parts of the value */
+    unsigned intpart = uvalue >> 16;
+    uint32_t fracpart = uvalue & 0xFFFF;
+    uint32_t scale = scales[decimals & 7];
+    fracpart = fix16_mul(fracpart, scale);
+    
+    if (fracpart >= scale)
+    {
+        /* Handle carry from decimal part */
+        intpart++;
+        fracpart -= scale;    
+    }
+    
+    /* Format integer part */
+    buf = itoa_loop(buf, 10000, intpart, true);
+    
+    /* Format decimal part (if any) */
+    if (scale != 1)
+    {
+        *buf++ = '.';
+        buf = itoa_loop(buf, scale / 10, fracpart, false);
+    }
+    
+    *buf = '\0';
+}
+
+fix16_t fix16_from_str(const char *buf)
+{
+    while (isspace(*buf))
+        buf++;
+    
+    /* Decode the sign */
+    bool negative = (*buf == '-');
+    if (*buf == '+' || *buf == '-')
+        buf++;
+
+    /* Decode the integer part */
+    uint32_t intpart = 0;
+    int count = 0;
+    while (isdigit(*buf))
+    {
+        intpart *= 10;
+        intpart += *buf++ - '0';
+        count++;
+    }
+    
+    if (count == 0 || count > 5
+        || intpart > 32768 || (!negative && intpart > 32767))
+        return fix16_overflow;
+    
+    fix16_t value = intpart << 16;
+    
+    /* Decode the decimal part */
+    if (*buf == '.' || *buf == ',')
+    {
+        buf++;
+        
+        uint32_t fracpart = 0;
+        uint32_t scale = 1;
+        while (isdigit(*buf) && scale < 100000)
+        {
+            scale *= 10;
+            fracpart *= 10;
+            fracpart += *buf++ - '0';
+        }
+        
+        value += fix16_div(fracpart, scale);
+    }
+    
+    /* Verify that there is no garbage left over */
+    while (*buf != '\0')
+    {
+        if (!isdigit(*buf) && !isspace(*buf))
+            return fix16_overflow;
+        
+        buf++;
+    }
+    
+    return negative ? -value : value;
+}
+

unittests/Makefile

@@ -5,10 +5,10 @@ CC = gcc
 CFLAGS = -g -O0 -I../libfixmath -Wall -Wextra -Werror
 
 # The files required for tests
-FIX16_SRC = ../libfixmath/fix16.c ../libfixmath/fix16_sqrt.c \
+FIX16_SRC = ../libfixmath/fix16.c ../libfixmath/fix16_sqrt.c ../libfixmath/fix16_str.c \
 	../libfixmath/fix16_exp.c ../libfixmath/fix16.h
 
-all: run_fix16_unittests run_fix16_exp_unittests
+all: run_fix16_unittests run_fix16_exp_unittests run_fix16_str_unittests
 
 clean:
 	rm -f fix16_unittests_????
@@ -55,3 +55,11 @@ run_fix16_exp_unittests: fix16_exp_unittests
 
 fix16_exp_unittests: fix16_exp_unittests.c $(FIX16_SRC)
 	$(CC) $(CFLAGS) $(DEFINES) -o $@ $^ -lm
+	
+# Tests for string conversion, run only in default config
+run_fix16_str_unittests: fix16_str_unittests
+	./fix16_str_unittests > /dev/null
+
+fix16_str_unittests: fix16_str_unittests.c $(FIX16_SRC)
+	$(CC) $(CFLAGS) $(DEFINES) -o $@ $^ -lm
+

unittests/fix16_str_unittests.c

@@ -0,0 +1,117 @@
+#include <fix16.h>
+#include <stdio.h>
+#include <math.h>
+#include <string.h>
+#include <stdbool.h>
+#include "unittests.h"
+
+int main()
+{
+    int status = 0;
+
+    {
+        COMMENT("Testing fix16_to_str corner cases");
+        char buf[13];
+        
+        fix16_to_str(fix16_from_dbl(1234.5678), buf, 4);
+        printf("1234.5678 = %s\n", buf);
+        TEST(strcmp(buf, "1234.5678") == 0);
+        
+        fix16_to_str(fix16_from_dbl(-1234.5678), buf, 4);
+        printf("-1234.5678 = %s\n", buf);
+        TEST(strcmp(buf, "-1234.5678") == 0);
+     
+        fix16_to_str(0, buf, 0);
+        TEST(strcmp(buf, "0") == 0);
+     
+        fix16_to_str(fix16_from_dbl(0.9), buf, 0);
+        TEST(strcmp(buf, "1") == 0);
+     
+        fix16_to_str(1, buf, 5);
+        printf("(fix16_t)1 = %s\n", buf);
+        TEST(strcmp(buf, "0.00002") == 0);
+        
+        fix16_to_str(-1, buf, 5);
+        printf("(fix16_t)-1 = %s\n", buf);
+        TEST(strcmp(buf, "-0.00002") == 0);
+        
+        fix16_to_str(65535, buf, 5);
+        printf("(fix16_t)65535 = %s\n", buf);
+        TEST(strcmp(buf, "0.99998") == 0);
+
+        fix16_to_str(65535, buf, 4);
+        printf("(fix16_t)65535 = %s\n", buf);
+        TEST(strcmp(buf, "1.0000") == 0);
+        
+        fix16_to_str(fix16_maximum, buf, 5);
+        printf("fix16_maximum = %s\n", buf);
+        TEST(strcmp(buf, "32767.99998") == 0);
+        
+        fix16_to_str(fix16_minimum, buf, 5);
+        printf("fix16_minimum = %s\n", buf);
+        TEST(strcmp(buf, "-32768.00000") == 0);
+    }
+
+    {
+        COMMENT("Testing fix16_from_str corner cases");
+    
+        TEST(fix16_from_str("1234.5678") == fix16_from_dbl(1234.5678));
+        TEST(fix16_from_str("-1234.5678") == fix16_from_dbl(-1234.5678));
+        TEST(fix16_from_str("   +1234,56780   ") == fix16_from_dbl(1234.5678));
+    
+        TEST(fix16_from_str("0") == 0);
+        TEST(fix16_from_str("1") == fix16_one);
+        TEST(fix16_from_str("1.0") == fix16_one);
+        TEST(fix16_from_str("1.0000000000") == fix16_one);
+        
+        TEST(fix16_from_str("0.00002") == 1);
+        TEST(fix16_from_str("0.99998") == 65535);
+        
+        TEST(fix16_from_str("32767.99998") == fix16_maximum);
+        TEST(fix16_from_str("-32768.00000") == fix16_minimum);
+    }
+    
+    {
+        COMMENT("Extended testing for whole range");
+        fix16_t value = fix16_minimum;
+        char testbuf[13];
+        char goodbuf[13];
+        
+        bool ok = true;
+        while (value < fix16_maximum)
+        {
+            double fvalue = fix16_to_dbl(value);
+        
+            /* Turns out we have to jump through some hoops to round
+            doubles perfectly for printing: 
+            http://stackoverflow.com/questions/994764/rounding-doubles-5-sprintf
+            */
+            fvalue = round(fvalue * 100000.)/100000.;
+        
+            snprintf(goodbuf, 13, "%0.5lf", fvalue);
+            fix16_to_str(value, testbuf, 5);
+            
+            if (strcmp(goodbuf, testbuf) != 0)
+            {
+                printf("Value (fix16_t)%d gave %s, should be %s\n", value, testbuf, goodbuf);
+                ok = false;
+            }
+            
+            fix16_t roundtrip = fix16_from_str(testbuf);
+            if (roundtrip != value)
+            {
+                printf("Roundtrip failed: (fix16_t)%d -> %s -> (fix16_t)%d\n", value, testbuf, roundtrip);
+                ok = false;
+            }
+        
+            value += 0x10001;
+        }
+        
+        TEST(ok);
+    }
+
+    if (status != 0)
+        fprintf(stdout, "\n\nSome tests FAILED!\n");
+
+    return status;
+}