From 56529d472f61dba8d01af27a792b5d14df1b2c2e Mon Sep 17 00:00:00 2001
From: Joseph Elliott Hand <jhand@hawaii.edu>
Date: Fri, 1 May 2026 17:25:39 -1000
Subject: Improve single unit identification

- Refactor into separate function
- Use array to store SI prefixes
- Add remaining SI prefixes

Signed-off-by: Joseph Elliott Hand <jhand@hawaii.edu>
---
 unit.h | 101 ++++++++++++++++++++++++++++++++---------------------------------
 1 file changed, 49 insertions(+), 52 deletions(-)

diff --git a/unit.h b/unit.h
index a4c8b9d..32a26c0 100644
--- a/unit.h
+++ b/unit.h
@@ -29,6 +29,7 @@ double get_unit_value(char const * string);
 
 #include <math.h>
 #include <regex.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
@@ -37,6 +38,32 @@ typedef struct {
 	double value;
 } Unit;
 
+double unit_prefixes[255] = {
+	['Q'] = 1e30,
+	['R'] = 1e27,
+	['Y'] = 1e24,
+	['Z'] = 1e21,
+	['E'] = 1e18,
+	['P'] = 1e15,
+	['T'] = 1e12,
+	['G'] = 1e9,
+	['M'] = 1e6,
+	['k'] = 1e3,
+	['h'] = 1e2,
+	['d'] = 1e-1,
+	['c'] = 1e-2,
+	['m'] = 1e-3,
+	['u'] = 1e-6,
+	['n'] = 1e-9,
+	['p'] = 1e-12,
+	['f'] = 1e-15,
+	['a'] = 1e-18,
+	['z'] = 1e-21,
+	['y'] = 1e-24,
+	['r'] = 1e-27,
+	['q'] = 1e-30
+};
+
 Unit units[] = {
 
     {"rad", 1},
@@ -141,6 +168,25 @@ get_token(char const * str, Token * token) {
 	return -1;
 }
 
+double
+resolve_unit_name(char const * name) {
+	
+	double prefix_amount = unit_prefixes[name[0]];
+	if(prefix_amount > 0) {
+		for (int j = 0; j < sizeof(units) / sizeof(units[0]); j++) {
+			if (strcmp(&name[1], units[j].abbr)) continue;
+			return prefix_amount * units[j].value;
+		}
+	}
+
+	for (int j = 0; j < sizeof(units) / sizeof(units[0]); j++) {
+		if (strcmp(name, units[j].abbr)) continue;
+		return units[j].value;
+	}
+	
+	return 0.0;
+}
+
 double
 get_unit_value(char const * string) {
 
@@ -190,56 +236,8 @@ get_unit_value(char const * string) {
 
 		if (tokens[i].type != NAME) goto error;
 
-		double unit_value = 0.0f;
-
-		for (int j = 0; j < sizeof(units) / sizeof(units[0]); j++) {
-			if (!strcmp(&tokens[i].value.str[1], units[j].abbr)) {
-				unit_value = units[j].value;
-				switch (tokens[i].value.str[0]) {
-					case 'k':
-						unit_value *= 1e3;
-						break;
-					case 'M':
-						unit_value *= 1e6;
-						break;
-					case 'G':
-						unit_value *= 1e9;
-						break;
-					case 'T':
-						unit_value *= 1e12;
-						break;
-					case 'c':
-						unit_value *= 1e-2;
-						break;
-					case 'm':
-						unit_value *= 1e-3;
-						break;
-					case 'u':
-						unit_value *= 1e-6;
-						break;
-					case 'n':
-						unit_value *= 1e-9;
-						break;
-					case 'p':
-						unit_value *= 1e-12;
-						break;
-					default:
-						goto error;
-				}
-				goto unit_found;
-			}
-		}
-
-		for (int j = 0; j < sizeof(units) / sizeof(units[0]); j++) {
-			if (!strcmp(tokens[i].value.str, units[j].abbr)) {
-				unit_value = units[j].value;
-				goto unit_found;
-			}
-		}
-
-		goto error;
-
-	unit_found:
+		double unit_value = resolve_unit_name(tokens[i].value.str);
+		if(unit_value == 0.0) goto error;
 
 		if (token_count <= i+1 || tokens[i + 1].type != EXP) {
 			value *= pow(unit_value, exp_sign);
@@ -256,8 +254,7 @@ get_unit_value(char const * string) {
 	return value;
 
 error:
-
-	fprintf(stderr, "unit.h: Invalid unit string: %s", string);
+	fprintf(stderr, "unit.h: Invalid unit string: %s\n", string);
 	return 0;
 }
 
-- 
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