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Merged
awjlogan merged 4 commits into from
Jan 14, 2026
+460 −87
Merged

[Util] Optimize conversion functions for Cortex-M0+ #41

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52d460e
[Util] Optimize conversion functions for Cortex-M0+
FredM67 Jan 8, 2026
48b6c13
Add const qualifier to read-only string parameters in util functions
FredM67 Jan 8, 2026
7deb87a
Use * 10 instead of shifts for multiplication
FredM67 Jan 8, 2026
8abbacc
Simplify utilFtoa: use direct multiply instead of shifts
FredM67 Jan 11, 2026
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1 change: 1 addition & 0 deletions .gitignore
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@
*.tgz
bin/emon32*
build/
build_bench/
cm-test-sine.csv
compile_commands.json
emon32_build_info.c
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203 changes: 119 additions & 84 deletions src/util.c
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Original file line number Diff line number Diff line change
Expand Up @@ -33,94 +33,111 @@ uint32_t utilStrlen(const char *pBuf) {
return charCnt;
}

/* Fast divide by 10 using shifts/adds only (no hardware divide) */
static inline uint32_t fastDiv10(uint32_t n) {
uint32_t q = (n >> 1) + (n >> 2);
q = q + (q >> 4);
q = q + (q >> 8);
q = q + (q >> 16);
q = q >> 3;
uint32_t r = n - ((q << 3) + (q << 1)); /* r = n - q*10 */
return q + ((r + 6) >> 4);
}

uint32_t utilItoa(char *pBuf, int32_t val, ITOA_BASE_t base) {
uint32_t charCnt = 0;
bool isNegative = false;
char *const pBase = pBuf;
char buf[12]; /* -2147483648 = 11 chars + null */
char *p = &buf[11];
uint32_t uval;
bool neg = false;

*p = '\0';

/* Handle 0 explicitly */
if (0 == val) {
*pBuf++ = '0';
*pBuf = '\0';
pBuf[0] = '0';
pBuf[1] = '\0';
return 2u;
}

/* Base 10 can be signed, and has a divide in */
if (ITOA_BASE10 == base) {
if (val < 0) {
isNegative = true;
val = -val;
neg = true;
uval = (uint32_t)(-val);
} else {
uval = (uint32_t)val;
}

while (0 != val) {
*pBuf++ = (val % 10u) + '0';
val = val / 10u;
charCnt++;
while (uval != 0) {
uint32_t q = fastDiv10(uval);
*--p = (char)('0' + (uval - ((q << 3) + (q << 1)))); /* uval - q*10 */
uval = q;
}

if (isNegative) {
*pBuf++ = '-';
charCnt++;
if (neg) {
*--p = '-';
}
} else {
const char itohex[] = "0123456789abcdef";
uint32_t val_u = (uint32_t)val;
static const char itohex[] = "0123456789abcdef";
uint32_t val_u = (uint32_t)val;

while (0 != val_u) {
*pBuf++ = itohex[(val_u & 0xFu)];
*--p = itohex[val_u & 0xFu];
val_u >>= 4;
charCnt++;
}
}

/* Terminate and return */
*pBuf = '\0';
charCnt++;
/* Copy to output buffer */
char *dst = pBuf;
uint32_t len = 0;
while (*p) {
*dst++ = *p++;
len++;
}
*dst = '\0';

utilStrReverse(pBase, charCnt - 1u);
return charCnt;
return len + 1u;
}

ConvInt_t utilAtoi(char *pBuf, ITOA_BASE_t base) {
bool isNegative = false;
uint32_t len;
uint32_t mulCnt = 1;
ConvInt_t conv = {false, 0};
uint32_t result = 0;
ConvInt_t conv = {false, 0};

if ('-' == *pBuf) {
isNegative = true;
pBuf++;
}

/* Reverse string and convert */
len = utilStrlen(pBuf);
utilStrReverse(pBuf, len);

/* Process left-to-right, no string reversal needed */
if (ITOA_BASE10 == base) {
while (*pBuf) {
if (!isnumeric(*pBuf)) {
return conv;
}
conv.val += ((*pBuf++) - '0') * mulCnt;
mulCnt *= 10;
}
if (isNegative) {
conv.val = -conv.val;
/* result = result * 10 + digit, using shifts for *10 */
result = (result << 3) + (result << 1) + (uint32_t)(*pBuf - '0');
pBuf++;
}
} else {
while (*pBuf) {
if (('a' <= *pBuf) && ('f' >= *pBuf)) {
conv.val += ((*pBuf) - 'a' + 10u) * mulCnt;
} else if (isnumeric(*pBuf)) {
conv.val += ((*pBuf) - '0') * mulCnt;
char c = *pBuf;
uint32_t digit;
if (('a' <= c) && ('f' >= c)) {
digit = (uint32_t)(c - 'a' + 10);
} else if (('A' <= c) && ('F' >= c)) {
digit = (uint32_t)(c - 'A' + 10);
} else if (isnumeric(c)) {
digit = (uint32_t)(c - '0');
} else {
return conv;
}
/* result = result * 16 + digit */
result = (result << 4) + digit;
pBuf++;
mulCnt *= 16;
}
}

conv.val = isNegative ? -(int32_t)result : (int32_t)result;
conv.valid = true;
return conv;
}
Expand All @@ -131,81 +148,99 @@ bool utilCharPrintable(const char c) {
}

uint32_t utilFtoa(char *pBuf, float val) {
uint32_t charCnt = 0;
bool isNegative = false;
char *const pBase = pBuf;
char buf[16]; /* Enough for -2147483648.99 + null */
char *p = &buf[15];
uint32_t units;
uint32_t decimals;
bool neg = false;

uint16_t decimals;
int32_t units;
*p = '\0';

if (val < 0.0f) {
isNegative = true;
val = qfp_fmul(val, -1.0f);
neg = true;
val = qfp_fmul(val, -1.0f);
}
decimals = qfp_float2int_z(qfp_fmul(val, 100.0f)) % 100;
units = qfp_float2int_z(val);

charCnt += 3u;
*pBuf++ = (decimals % 10) + '0';
decimals = decimals / 10;
*pBuf++ = (decimals % 10) + '0';
*pBuf++ = '.';

if (0 == units) {
*pBuf++ = '0';
charCnt++;
/* Extract integer and fractional parts */
units = (uint32_t)qfp_float2int_z(val);
/* decimals = (val * 100) - (units * 100), using shifts for *100 */
uint32_t val100 = (uint32_t)qfp_float2int_z(qfp_fmul(val, 100.0f));
uint32_t units100 =
(units << 6) + (units << 5) + (units << 2); /* units * 100 */
decimals = val100 - units100;

/* Write decimals (always 2 digits) using fast division */
uint32_t q = fastDiv10(decimals);
*--p = (char)('0' + (decimals - ((q << 3) + (q << 1)))); /* decimals % 10 */
*--p = (char)('0' + q); /* tens digit */
*--p = '.';

/* Write integer part */
if (units == 0) {
*--p = '0';
} else {
while (units != 0) {
q = fastDiv10(units);
*--p = (char)('0' + (units - ((q << 3) + (q << 1)))); /* units % 10 */
units = q;
}
}

while (0 != units) {
*pBuf++ = (units % 10) + '0';
units = units / 10;
charCnt++;
if (neg) {
*--p = '-';
}

if (isNegative) {
*pBuf++ = '-';
charCnt++;
/* Copy to output buffer */
char *dst = pBuf;
uint32_t len = 0;
while (*p) {
*dst++ = *p++;
len++;
}
*dst = '\0';

/* Terminate and return */
*pBuf = '\0';
charCnt++;

utilStrReverse(pBase, charCnt - 1u);
return charCnt;
return len + 1u;
}

ConvFloat_t utilAtof(char *pBuf) {
bool isNegative = false;
uint32_t len = 0;
uint32_t mulCnt = 1u;
uint32_t fraction = 0u;
uint32_t intPart = 0;
uint32_t fracPart = 0;
uint32_t fracDiv = 1;
bool inFraction = false;
ConvFloat_t conv = {false, 0.0f};

if ('-' == *pBuf) {
isNegative = true;
pBuf++;
}
len = utilStrlen(pBuf);
utilStrReverse(pBuf, len);

/* Process left-to-right, no string reversal needed */
while (*pBuf) {
const char c = *pBuf++;
/* Allow period/comma delimit, divide down if found */
if (('.' == c) || (',' == c)) {
fraction = mulCnt;
inFraction = true;
} else if (isnumeric(c)) {
const float toAdd = qfp_uint2float((c - '0') * mulCnt);
conv.val = qfp_fadd(conv.val, toAdd);
mulCnt *= 10;
uint32_t digit = (uint32_t)(c - '0');
if (inFraction) {
/* fracPart = fracPart * 10 + digit */
fracPart = (fracPart << 3) + (fracPart << 1) + digit;
fracDiv = (fracDiv << 3) + (fracDiv << 1);
} else {
/* intPart = intPart * 10 + digit */
intPart = (intPart << 3) + (intPart << 1) + digit;
}
} else {
/* Invalid character found */
return conv;
}
}

if (0 != fraction) {
conv.val = qfp_fdiv(conv.val, qfp_uint2float(fraction));
/* Convert to float only at the end */
conv.val = qfp_uint2float(intPart);
if (fracDiv > 1u) {
conv.val = qfp_fadd(
conv.val, qfp_fdiv(qfp_uint2float(fracPart), qfp_uint2float(fracDiv)));
}

if (isNegative) {
Expand Down
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