ascii.h

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/*-----------------------------------------------------------------------
 * ascii.h
 *
 *   Portions Copyright (c) 1999-2024, PostgreSQL Global Development Group
 *
 * src/include/utils/ascii.h
 *
 *-----------------------------------------------------------------------
 */
 
#ifndef _ASCII_H_
#define _ASCII_H_
 
#include "port/simd.h"
 
extern void ascii_safe_strlcpy(char *dest, const char *src, size_t destsiz);
 
/*
 * Verify a chunk of bytes for valid ASCII.
 *
 * Returns false if the input contains any zero bytes or bytes with the
 * high-bit set. Input len must be a multiple of the chunk size (8 or 16).
 */
static inline bool
is_valid_ascii(const unsigned char *s, int len)
{
    const unsigned char *const s_end = s + len;
    Vector8     chunk;
    Vector8     highbit_cum = vector8_broadcast(0);
#ifdef USE_NO_SIMD
    Vector8     zero_cum = vector8_broadcast(0x80);
#endif
 
    Assert(len % sizeof(chunk) == 0);
 
    while (s < s_end)
    {
        vector8_load(&chunk, s);
 
        /* Capture any zero bytes in this chunk. */
#ifdef USE_NO_SIMD
 
        /*
         * First, add 0x7f to each byte. This sets the high bit in each byte,
         * unless it was a zero. If any resulting high bits are zero, the
         * corresponding high bits in the zero accumulator will be cleared.
         *
         * If none of the bytes in the chunk had the high bit set, the max
         * value each byte can have after the addition is 0x7f + 0x7f = 0xfe,
         * and we don't need to worry about carrying over to the next byte. If
         * any input bytes did have the high bit set, it doesn't matter
         * because we check for those separately.
         */
        zero_cum &= (chunk + vector8_broadcast(0x7F));
#else
 
        /*
         * Set all bits in each lane of the highbit accumulator where input
         * bytes are zero.
         */
        highbit_cum = vector8_or(highbit_cum,
                                 vector8_eq(chunk, vector8_broadcast(0)));
#endif
 
        /* Capture all set bits in this chunk. */
        highbit_cum = vector8_or(highbit_cum, chunk);
 
        s += sizeof(chunk);
    }
 
    /* Check if any high bits in the high bit accumulator got set. */
    if (vector8_is_highbit_set(highbit_cum))
        return false;
 
#ifdef USE_NO_SIMD
    /* Check if any high bits in the zero accumulator got cleared. */
    if (zero_cum != vector8_broadcast(0x80))
        return false;
#endif
 
    return true;
}
 
#endif                          /* _ASCII_H_ */