What the developer wrote
Authored by Lőrinc
field: serialize elements by word
The byte assignments replaced nested nibble loops before the endian write helpers existed.
Pack the 5x52 limbs into four 64-bit words and the 10x26 limbs into eight 32-bit words, then use those helpers.
This matches the scalar serializers and keeps the output unchanged.
Benchmarks indicate no measurable performance regression.
What changed, and why it matters
This commit is a clean-up rewrite of how internal numeric values are converted into 32-byte output inside the secp256k1 cryptography library. It replaces many byte-by-byte shift-and-mask operations with a smaller number of whole-word writes using existing helper functions. The commit message explicitly states the output is unchanged, and the diff shows a direct mechanical refactoring with no change to inputs, preconditions, or callers.
No security action needed. Treat as a normal code-quality / maintainability change. Standard review and regression testing are sufficient.
Security signals we found
No strong security signals were identified.
Evidence from the diff
The patch refactors secp256k1_fe_impl_get_b32() in both the 10x26 and 5x52 field implementations. The old code extracted each output byte individually through nested shifts and masks; the new code assembles 32-bit or 64-bit words from the limbs and writes them via secp256k1_write_be32 / secp256k1_write_be64. The function contract (input must be normalized, output is 32 bytes big-endian) is preserved, and no other code paths are modified. There is no evidence of a security bug, bounds issue, or behavior change.
Changed components
src/field_10x26_impl.hsrc/field_5x52_impl.hInspect captured patch +12 / −64
diff --git a/src/field_10x26_impl.h b/src/field_10x26_impl.h
index aa45434..abd17aa 100644
--- a/src/field_10x26_impl.h
+++ b/src/field_10x26_impl.h
@@ -303,38 +303,14 @@ static int secp256k1_fe_impl_set_b32_limit(secp256k1_fe *r, const unsigned char
/** Convert a field element to a 32-byte big endian value. Requires the input to be normalized */
static void secp256k1_fe_impl_get_b32(unsigned char *r, const secp256k1_fe *a) {
- r[0] = (a->n[9] >> 14) & 0xff;
- r[1] = (a->n[9] >> 6) & 0xff;
- r[2] = ((a->n[9] & 0x3F) << 2) | ((a->n[8] >> 24) & 0x3);
- r[3] = (a->n[8] >> 16) & 0xff;
- r[4] = (a->n[8] >> 8) & 0xff;
- r[5] = a->n[8] & 0xff;
- r[6] = (a->n[7] >> 18) & 0xff;
- r[7] = (a->n[7] >> 10) & 0xff;
- r[8] = (a->n[7] >> 2) & 0xff;
- r[9] = ((a->n[7] & 0x3) << 6) | ((a->n[6] >> 20) & 0x3f);
- r[10] = (a->n[6] >> 12) & 0xff;
- r[11] = (a->n[6] >> 4) & 0xff;
- r[12] = ((a->n[6] & 0xf) << 4) | ((a->n[5] >> 22) & 0xf);
- r[13] = (a->n[5] >> 14) & 0xff;
- r[14] = (a->n[5] >> 6) & 0xff;
- r[15] = ((a->n[5] & 0x3f) << 2) | ((a->n[4] >> 24) & 0x3);
- r[16] = (a->n[4] >> 16) & 0xff;
- r[17] = (a->n[4] >> 8) & 0xff;
- r[18] = a->n[4] & 0xff;
- r[19] = (a->n[3] >> 18) & 0xff;
- r[20] = (a->n[3] >> 10) & 0xff;
- r[21] = (a->n[3] >> 2) & 0xff;
- r[22] = ((a->n[3] & 0x3) << 6) | ((a->n[2] >> 20) & 0x3f);
- r[23] = (a->n[2] >> 12) & 0xff;
- r[24] = (a->n[2] >> 4) & 0xff;
- r[25] = ((a->n[2] & 0xf) << 4) | ((a->n[1] >> 22) & 0xf);
- r[26] = (a->n[1] >> 14) & 0xff;
- r[27] = (a->n[1] >> 6) & 0xff;
- r[28] = ((a->n[1] & 0x3f) << 2) | ((a->n[0] >> 24) & 0x3);
- r[29] = (a->n[0] >> 16) & 0xff;
- r[30] = (a->n[0] >> 8) & 0xff;
- r[31] = a->n[0] & 0xff;
+ secp256k1_write_be32(&r[0], (a->n[9] << 10) | (a->n[8] >> 16));
+ secp256k1_write_be32(&r[4], (a->n[8] << 16) | (a->n[7] >> 10));
+ secp256k1_write_be32(&r[8], (a->n[7] << 22) | (a->n[6] >> 4));
+ secp256k1_write_be32(&r[12], (a->n[6] << 28) | (a->n[5] << 2) | (a->n[4] >> 24));
+ secp256k1_write_be32(&r[16], (a->n[4] << 8) | (a->n[3] >> 18));
+ secp256k1_write_be32(&r[20], (a->n[3] << 14) | (a->n[2] >> 12));
+ secp256k1_write_be32(&r[24], (a->n[2] << 20) | (a->n[1] >> 6));
+ secp256k1_write_be32(&r[28], (a->n[1] << 26) | a->n[0]);
}
SECP256K1_INLINE static void secp256k1_fe_impl_negate_unchecked(secp256k1_fe *r, const secp256k1_fe *a, int m) {
diff --git a/src/field_5x52_impl.h b/src/field_5x52_impl.h
index 0e0e2d6..6a2987e 100644
--- a/src/field_5x52_impl.h
+++ b/src/field_5x52_impl.h
@@ -269,38 +269,10 @@ static int secp256k1_fe_impl_set_b32_limit(secp256k1_fe *r, const unsigned char
/** Convert a field element to a 32-byte big endian value. Requires the input to be normalized */
static void secp256k1_fe_impl_get_b32(unsigned char *r, const secp256k1_fe *a) {
- r[0] = (a->n[4] >> 40) & 0xFF;
- r[1] = (a->n[4] >> 32) & 0xFF;
- r[2] = (a->n[4] >> 24) & 0xFF;
- r[3] = (a->n[4] >> 16) & 0xFF;
- r[4] = (a->n[4] >> 8) & 0xFF;
- r[5] = a->n[4] & 0xFF;
- r[6] = (a->n[3] >> 44) & 0xFF;
- r[7] = (a->n[3] >> 36) & 0xFF;
- r[8] = (a->n[3] >> 28) & 0xFF;
- r[9] = (a->n[3] >> 20) & 0xFF;
- r[10] = (a->n[3] >> 12) & 0xFF;
- r[11] = (a->n[3] >> 4) & 0xFF;
- r[12] = ((a->n[2] >> 48) & 0xF) | ((a->n[3] & 0xF) << 4);
- r[13] = (a->n[2] >> 40) & 0xFF;
- r[14] = (a->n[2] >> 32) & 0xFF;
- r[15] = (a->n[2] >> 24) & 0xFF;
- r[16] = (a->n[2] >> 16) & 0xFF;
- r[17] = (a->n[2] >> 8) & 0xFF;
- r[18] = a->n[2] & 0xFF;
- r[19] = (a->n[1] >> 44) & 0xFF;
- r[20] = (a->n[1] >> 36) & 0xFF;
- r[21] = (a->n[1] >> 28) & 0xFF;
- r[22] = (a->n[1] >> 20) & 0xFF;
- r[23] = (a->n[1] >> 12) & 0xFF;
- r[24] = (a->n[1] >> 4) & 0xFF;
- r[25] = ((a->n[0] >> 48) & 0xF) | ((a->n[1] & 0xF) << 4);
- r[26] = (a->n[0] >> 40) & 0xFF;
- r[27] = (a->n[0] >> 32) & 0xFF;
- r[28] = (a->n[0] >> 24) & 0xFF;
- r[29] = (a->n[0] >> 16) & 0xFF;
- r[30] = (a->n[0] >> 8) & 0xFF;
- r[31] = a->n[0] & 0xFF;
+ secp256k1_write_be64(&r[0], (a->n[4] << 16) | (a->n[3] >> 36));
+ secp256k1_write_be64(&r[8], (a->n[3] << 28) | (a->n[2] >> 24));
+ secp256k1_write_be64(&r[16], (a->n[2] << 40) | (a->n[1] >> 12));
+ secp256k1_write_be64(&r[24], (a->n[1] << 52) | a->n[0]);
}
SECP256K1_INLINE static void secp256k1_fe_impl_negate_unchecked(secp256k1_fe *r, const secp256k1_fe *a, int m) {
Why this scored 15/100
Community notes
Notes can correct, qualify, or add evidence to the AI analysis. Every note shown here has been validated by a human moderator.
The AI analysis stands alone for now. Submit a note if you can add evidence or important context.