Use uint64 for some loop counters

src/fft_common.c

@@ -28,7 +28,7 @@ C_KZG_RET expand_root_of_unity(blst_fr *roots, const blst_fr *root_of_unity, con
     roots[0] = fr_one;
     roots[1] = *root_of_unity;
 
-    for (int i = 2; !fr_is_one(&roots[i - 1]); i++) {
+    for (uint64_t i = 2; !fr_is_one(&roots[i - 1]); i++) {
         ASSERT(i <= width, C_KZG_ERROR);
         blst_fr_mul(&roots[i], &roots[i - 1], root_of_unity);
     }
@@ -40,7 +40,7 @@ C_KZG_RET expand_root_of_unity(blst_fr *roots, const blst_fr *root_of_unity, con
 // Create a reversed list of Fr provided
 // `width` is one less than the length of `roots`
 C_KZG_RET reverse(blst_fr *out, const blst_fr *roots, const uint64_t width) {
-   for (int i = 0; i <= width; i++) {
+   for (uint64_t i = 0; i <= width; i++) {
        out[i] = roots[width - i];
    }
 

src/fft_common_test.c

@@ -30,9 +30,9 @@ void roots_of_unity_is_the_expected_size(void) {
 
 void roots_of_unity_are_plausible(void) {
     blst_fr r;
-    for (unsigned int i = 0; i < NUM_ROOTS; i++) {
+    for (int i = 0; i < NUM_ROOTS; i++) {
         blst_fr_from_uint64(&r, scale2_root_of_unity[i]);
-        for (unsigned int j = 0; j < i; j++) {
+        for (int j = 0; j < i; j++) {
             blst_fr_sqr(&r, &r);
         }
         TEST_CHECK(true == fr_is_one(&r));
@@ -83,7 +83,7 @@ void expand_roots_is_plausible(void) {
 
 void new_fft_settings_is_plausible(void) {
     // Just test one (largeish) value of scale
-    unsigned int scale = 21;
+    int scale = 21;
     unsigned int width = 1 << scale;
     blst_fr prod;
     FFTSettings s;

src/poly.c

@@ -32,6 +32,7 @@ void poly_free(poly p) {
 
 void poly_eval(blst_fr *out, const poly *p, const blst_fr *x) {
     blst_fr tmp;
+    uint64_t i;
 
     if (p->length == 0) {
         fr_from_uint64(out, 0);
@@ -42,9 +43,12 @@ void poly_eval(blst_fr *out, const poly *p, const blst_fr *x) {
 
     // Horner's method
     *out = p->coeffs[p->length - 1];
-    for (int i = p->length - 2; i >= 0; i--) { // needs to be uint64_t?
+    i = p->length - 2;
+    while (true) {
         blst_fr_mul(&tmp, out, x);
         blst_fr_add(out, &tmp, &p->coeffs[i]);
+        if (i == 0) break;
+        --i;
     }
 }